I totally agree with you, I'm just presenting it from their perspective, you can bet that response is closely tailored by their lawyers.
All in all the practice of telling customers something is operating as designed is an extremely poor business practice from a PR standpoint and I try to communicate that to my clients but its difficult because thats the legally safe response. You're right, customers who have been long labored by problems like these would much rather hear "This is a problem with the transmission, DBW, whatever, I'm extremely sorry but there isn't anything we can do" than "thats operating as its designed" which makes the customer feel like an idiot, its like saying "You idiot, why don't you like our perfectly engineered system?". Its just admitting fault in a situation like this is not smart from a legal or liability standpoint. If dealers tell customers theres a problem then that gives fuel for class action lawsuits etc, if you were a lawyer and Lexus was your client you'd tell them the same thing.
Its not right, but its business.