I dunno what to tell you, dude... look at any phones that have come out in the last 4 years... they sell accessories, but no ram upgrades for them. There simply hasn't been enough demand to do it anymore, I think.
As for your memory problems... look around the forum to see how others deal with these "problems". With a little bit of memory management, things run perfectly fine. I never get memory errors, haven't had them in my last few htc phones because I've learned my way around the memory thing by now.
Honestly, even if they offered it, I wouldn't pay to have them install new chips in my phone.
Close programs, don't install too many plugins, and if need be, run that oxios program that frees up the file system cache.