Funny, I've become more flexible with riding, and I don't do any stretching before or after riding. When I first started riding again 3 yrs ago, I couldn't reach the floor with fingertips. Now, I can always touch the floor with fingertips, and can go even further after a ride.

I suspect it has to do with the positions I'm in when riding. Specifically, using back and leg muscles while in a more aero/tucked position has led to greater flexibility and range of those muscles than before.

Doesn't make a whole of sense at first, huh!