I'm not sure why you think that. I had known of OMGPOP for a few years prior to Draw Something because some friends and I played their tetris game. To have one hit like Draw Something in those couple of years doesn't suggest to me they would've had much further success.
Are you talking about iOS game companies or other game companies? I'm talking about iOS game companies.
Also, I didn't say it was a guarantee, but it is far far easier. Also, remember the scale of Draw Something. Over 100 million downloads in the first year.