The idea that 5M/month Draw Something care about the Zynga purchase is ludicrous. It seems Zynga has made some annoying changes to the game, at least for those that use Facebook to login, but even so.
I think the only story here is that Zynga overpaid for something that was peaking. They may purchased OMGPOP just in case it turned into something huge. There's plenty of that going on (cough Instragram cough).
I've tried Draw Something. It's amusing and I can see the appeal but from all usage patterns I've seen the game has a pretty short shelf life. A game with a short shelf life is going to lose lots of customers once it peaks. It's inevitable.
As for how easy it is to make a game, that's actually hard. I believe you should also separate "normal" games from "social" games here as both are radically different.
Normal games are like blockbuster movies. You want people to buy up big. You deliberately build up the hype. There is very little in the way of long tail in revenue in most cases (other than sequels). I consider this a fairly "honest" or ethical practice because you pay the sticker price and you have your fun.
Social games are more like TV shows. You're trying to build a persistent audience and you're all about the long tail. The part that bothers me is the psychological trickery that goes into this. Social games are really about manipulating the psychological triggers for addiction and I don't really see a distinction between this and, say, gambling addiction.
Some people spend an awful lot on these games (I believe Zynga calls people who spend over $10k "whales" [1]). Zynga and similar companies like to whitewash this with "maybe they're just rich". I believe they know better. They are (IMHO) preying on the weak and those arguably with mental health problems ("it's not unethical, it's funethical!").
Successful social games are all about Big Data. Figuring out what works, what doesn't, analyzing your customer usage and adjusting to maximize revenue and retention.
They're not even "games" really. They're just exercises in repetition.
Anyway, rant aside, I don't like Zynga either but please don't confuse the OMGPOP purchase with a short shelf-life peaking purchase.
[1]: http://www.businessweek.com/magazine/zyngas-quest-for-bigspe...