Does Mark Zuckerberg work out? How about John Lasseter?
It honestly doesn't seem fitness has any relation what-so-ever to success but I'd be happy to be proven wrong with actual data rather than anecdotes.
Richard Branson's main piece of productivity advice is "work out"[2].
A strong counterexample would be Warren Buffett, who was once the world's richest man, never worked out, and ate terribly.
Ultimately though it's best to look at the studies other responders to your post cited, which do show some correlation between exercise and mental performance.
Edit: forgot my links
[1]: http://venturebeat.com/2009/10/02/mark-zuckerberg-the-evolut...
Here is a video where Branson says he achieves "twice as much" on a day when he works out compared to a day when he doesn't exercise: http://www.youtube.com/watch?v=QFjgMKwpz_k
The ways exercise benefits the brain was discussed on HN before multiple times.
http://news.ycombinator.com/item?id=3620529 How Exercise Fuels the Brain (well.blogs.nytimes.com)
http://news.ycombinator.com/item?id=3047554 How Exercise Can Strengthen the Brain (well.blogs.nytimes.com)
A search for 'exercise brain' returns many more results. Now it's up to 'is improving your brain function cornerstone to success?'
But the kind self-control you need for fitness could also help you become successful. If so, there might indeed be some correlation between fitness and success.
I don't think your lack of pain has anything to do with your working out. More likely luck, genetics, or lack of other activities that would lead to pain.
http://venturebeat.com/2009/10/02/mark-zuckerberg-the-evolut...