Yea, RPN is a nice feature to have. I can get along without it, but I much prefer a calculator with it.  I've played with a couple other calculators back then that claimed to use RPN, but they didn't have the four-deep stack that HP has, and were fairly useless.

Mind you, I started with a TI-30, then progressed to a TI-58C. Lots of buddies had a TI-58C or TI-59 (the TI programmable that read the wee little magnetic strips). When the price on the HP-41C's and CV's came down, a lot of us went for those because the TI's didn't hold up under hard use. (EE students used their calculators all day, every day...). Right after a bunch of us got our 41's, the 15C came out and at about half the price of the 41's. If I didn't already have a 41 when it came out, I would have gotten a 15C immediately.

The biggest reason I think so many guys loved the HP wasn't just their nerd-baiting features, it was the keyboards and ergonomics. When you're cranking through lots of computations, it really helps to know when you've pressed a key, that the key didn't bounce, etc. TI keys were notoriously "bouncy" and repeated after they started getting some wear on them.