In answer to your question no you can't, in answer to your title, yes It would be good if you could though.
more and more programs are allowing this because it keeps it the money within the company. I would expect Google to jump on the bandwagon, unfortunately they dont offer it atm.
what would be really nice is if I didn't have to re-type my password for every single google service that I use - adwords, adsense, gmail, analytics. why can't they tie all that stuff into one login system...