You're right; it's not a big issue--it's just that, in the year 2007, I'm guessing SQ didn't HAVE to do this--do you think their IT department can't handle having some people with SQ FF#s and some with regular usernames?
SQ made a choice that, ironically enough, doesn't make it easier for all of their customers to buy a ticket--in fact, it adds another annoying card to my wallet, another email I don't want to get, etc.....
Funny enough, these Star Alliance airlines seem to forget that there are thousands of pax who are using the alliance's other airlines to book tickets, but aren't part of THAT airline's FFP.
Ugh.