they shouldn't be, but there's a practical difference in how often your house gets raided by FBI agents.

if a Tor user uses your exit node to email a bomb threat or access child porn, it's your source IP that shows up. the FBI should check your IP against the registry of exit node IPs, but if they don't it's still your door getting kicked in.

Exactly - and I've noticed there aren't very many exit nodes at all, small enough that I can start to recognize them by name.

Yea, there is only about 1000 (actually 1300, I just checked) exits - out of only ~6000 nodes total, the Tor network is actually kinda small.

So I guess the question is, how would one scale the number of nodes? Isn't that really what's needed then?

Yes, and it's needed. Running relays or exits helps the network.