Wow, as one of the "pioneers" of the SaaS model, and a highly successful bootstrapped startup for 10+ years, I would have to say... yes, I would imagine you are one of very few people in this community who would have never heard of 37signals.
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.