bringing it to other platforms would also bring more users into the google ecosystem...i thought they'd be all over it. plus so many of my n00b friends would stop texting me and just send me a gchat msg
The problem with Google Talk is that you need a good data connection. SMS still uses the cellular network and does not need a data connection to work.
This is an issue. Last year at Coachella (I had Tmo) I could not get a data connection to use Google Voice and text my friends when we got separated. I had a cell connection, but I could not send texts out because I had blocked all texts since I had Google Voice. When you do not have data with GV basically you use SMS/cell texting, and GV does not work and will not show your GV number (the number that I had given to all my friends) when you call.
Luckily I was able to use my real cell, non-GV number, but it took like 5 tries for them to answer because they did not recognize the number. This year I have Verizon, but I have prepared by buying 200 texts just in case I get no data at the fest.