While I think it's good to start with freeware to learn game design, you can still work in flash and at least make some money from it since flash games are add supported.
As for downloadable PC games, there currently doesn't seem to be much of a market for small for-purchase games, so you probably shouldn't enter that market until you have enough skill to make a larger project or are willing to risk paving the way in a less tested market.
One think I've heard (In fact, I heard it here:
http://www.gamasutra.com/php-bin/news_index.php?story=24686), is that when trying to make money from indie games, especially in markets such as flash games and iPhone games, quantity is important. You need to have quick development times. As you said, you can't expect to support yourself on one big hit flash game as it's unlikely one game will be that successful, but if you can make many good games quickly, you have a better chance of having a consistent revenue stream.
Of course, not having "gone commercial" yet myself (except for the occasional foray into flash game design), I probably don't have the best advice.