Am I the only one who had never heard of 37signals before?
The HN/YC model of a "startup" is something that is growing rapidly, as per http://www.paulgraham.com/growth.html, so perhaps 37signals was never a startup in the HN use of the term ;-)
But when I mention Basecamp, they say "Oh Basecamp!! Of course! We love Basecamp!"
World-wide, Basecamp is much bigger brand than 37signals.
Just because you've had success doesn't mean you know everything about even your success or why you achieved it. Be humble, even while educating and talking about your achievements.