This link works fine for me on my Mac using Google Chrome. It might be a pop-up that is blocked for you...
Chrome also has a built in Flash plug-in, I didn't check if they use Flash for the pop-up login, but this is a login page for Creative Cloud. You can bypass it by logging in here:
The product isn't shipping yet, but you can get it for $29.99 if you own CS3 or newer (through the link above)
I'm logged in, that's not the issue. The problem is that once logged in, there are no apps shown on a Mac. The cause of the 404 is a little mysterious to me, as the browser doesn't record a failed attempt to do anthing. Maybe some sort of internal 404? Seems like a bug to me.
Have you tried another browser? What Apps are you looking for? The Adobe Touch Apps, CS6, Creative Cloud? The offerings for Mac and Windows are identical when it comes to CS6 and Creative Cloud.