From my response to this comment on the blog:

If "swinging for the fences" requires 24/7 work, chances are you're not focused enough, not validating your ideas fast enough, and from my experience, you're probably wasting a huge amount of your time doing on inefficient work or unnecessary stuff that will be scrapped entirely. That being said, starting small and focused does not eliminate the possibility of building something big.

To build on your baseball analogy-- who wins more games, the team with the most homeruns or the team with the most hits? 37 Signals proves the analogy-- a series of simple, focused, products, that started small and have achieved massive success.