My two cents regarding Engine Oil Sludging.
This has been going on for as long as gasoline engines have been used in automobiles or even gasoline engines used in a stationary location. If you read the article, from The Auto Channel, I posted you will now have a better understanding of the causes of engine sludge.
The following is a Honda Civic engine. It's not that I could not find a Toyota engine to show but it is really to show you what sludge looks like and that it can happen to any make of vehicle. 
This is from a V-6 Camry.  The oil pump pick-up screen is totally plugged with sludge.  If let alone the engine would have starved for oil and self destructed.
You came this far into the site to find out "why me" and what can I do now that I've been told its my problem by the Toyota dealer or their representative.
Is Toyota to blame for some design problem, maybe.
Are you to blame for the way the engine was maintained, maybe.
If you examine the factory recommend service schedule and warranty requirements it states that your warranty will remain in effect for the term of the warranty coverage based on the model year coverage. It states that at specific mileage or month intervals you are required to do certain maintenance checks or part replacements to the vehicle and you are not limited to having the dealer perform these for you. It states that you, your neighbor, the local independent repair shop or the authorized Toyota dealer can so these for you. If you choose not to have the dealer do the work then you need to insure that quality parts are used, receipts kept with mileage and dates they were performed retained by you, and that if something done during the maintenance affects the vehicle, the responsibility may rest with you.
In English it means that you do not have to have the dealer do all the work, you have to use quality parts, keep all receipts and do them on time. Failure to leave anyone of these steps out and you may be out of luck as far as Toyota is concerned. Its not that they are looking for loopholes but they do tell you how to stay in the guidelines and if you take the responsibility to do the maintenance on your own, you imply that you understand the requirements.
I know that sounds like I'm a factory lackey but I don't work for or represent Toyota Motor Company in any fashion, its just that the 30 years of dealing with auto warranties (10 years with Toyota dealers) I know the things the factory looks for. So whether you feel it right or wrong its printed in the owners manual you had before you left with the new vehicle from the dealership.
My contention is that the language they are now using is somewhat vague. If Toyota says that you can maintain the vehicle they are responsible for telling you what is acceptable for replacement parts, a list of recommended ones and the ones that they cannot recommend. Their failure to do so sets the precedence for the use of any brand of part or lubricant ( as long as it is manufactured for your Toyota and the correct oil viscosity for your area) qualifies as a "quality part" and meets their maintenance requirements. When the dealer or the factory representative says that poor quality parts must have been used they don't have a "leg" to stand on since they never stated what quality parts means. They may assume that only their parts are "quality" but never state in writing so that you can comply.
Now for the record keeping. Just like you record each check you write, or you should so that you always know the balance of your checkbook, your vehicle needs the same treatment. If you use a dealer or some local business they will keep those records for you, at least most national chain stores that I am familiar with do that. They know the importance of record keeping for their sake and yours. When you do things yourself or go down to some local gas station for the Saturday oil change you should keep those records. Now why is Toyota so adamant about records. The reason is that people will tend to stretch the truth when they are in trouble or in danger of spending money for something they did wrong. Its not to say that all owners fall in to these categories, but there are many in the "its not my fault, I did not know" sector of mankind. Toyota like other manufactures of consumer goods will stand behind the product, if its taken care of by their standards, not changing the oil in 15,000 or more miles can cause damage that they cannot control, that's why records are needed. They are actually looking out for themselves and you, so that with those records the actual cause of the problem can be determined, to both parties satisfaction.
You may not believe this but Toyota or any other manufacture of auto/trucks will do more for the customer if the customer did all or more than they asked, regarding maintenance. They will also be the first ones to bail out when given that chance or when no real effort was made to protect their product.
That's my two cents on "who's to blame" regarding sludge. Now if you suffer from that condition or have had the problem repaired at you expense you need to call or visit the local Toyota dealer. Toyota has begun repairing the engines at their expense starting in Feb. 02 and more so after April 3, 02.

Automotive News article 4/3/02 & 2/8/02