You aren't forced.
You have a choice between paying and grinding.
Do you look at league of legends and go "OH GOD. THEY ARE FORCING ME TO GRIND MILLIONS OF IP TO UNLOCK CHAMPIONS". No. It's OPTIONAL.
---------- Post added 2013-07-02 at 10:05 AM ----------
You need to update your info. Zen costs are 300 AD now. So it's about 150,000 AD. And the limit is pretty pointless as you can get as many refined as you want via the auction house.