I know this is an old message, but the answer is because you're not in the USA. I'm in the UK, and I don't see the download button either. I don't know which countries get the download. The solution is to use a proxy server .
Edit: I see from a later post that you got an explanation from Google. Teach me to read to the end of the thread before posting . The proxy server advice stands, though.
Regards
arian