I at least slow down and ask if they need help. People on the trail back home do the same thing. I'll be stopped for no "good" reason (usually to grab a snack) and people ask if I'm okay and need anything.

I once fell on some ice and went over the bars...I think. I was fine, just a little shaken and scraped up. An older guy (turns out he'd just moved up from Texas) stopped, asked if I was okay, and helped me get the chain back on the bike.
Now that I think about it, the only ones who don't at least ask if I need help are the guys about my age who are off in their own little world of speed...Maybe it's a regional thing?