It's for the very reason that you mention i.e. that veto hurts OBAMA, but as far as Abbas is concerned it hurts him not at all. After all, what's the difference between (a) putting in the application and being knocked back and (b) not putting in the application at all? Answer: Nothing.
Toronto nightclub shooting leaves at least 2 dead, 3 wounded (AP)
from the article: Abbas to seek full UN recognition despite Western pressure