Getting past 8 MB on a A500 is hard even with the best expansions. 16 MB is the limit of the MC68000. So I dault this value really reflects how it works.
Microsoft can't make good software nor offer sane licenses. And I prefer wired.
To most people (not to me) "the internet" means the the web and I'm just guessing 16MB is the minimum amount of RAM you need to run a browser. To do just FTP, and IRC and SSH/Telnet I'd think 4MB would be enough. I just said 16MB to cover all bases.