A little history:
FDNY EMS was originally NYC EMS, under NYC HHC. They were their own entity. They were happy. They had great equipment, decent pay, and good working conditions. Then, FDNY absorbed them in 1996 (I think). They've cannabilized EMS, and have allocated the lion's share of funding to the suppression side. FDNY EMS was made the victim of having an expired contract for many years stuck at the same pay/benefits, having to work with substandard equipment in various states of disrepair, and increasingly deplorable working working conditions - copious mandatory OT, taking away of paid time off as punitive measures, numerous unneccesary NOI's (notice of infraction), welfare wages to name a few.
FDNY EMS didn't even have uniform status and a real union (local 2507) until just a few years ago, and were finally able to negotiate a new contract. To make matters worse, as they were working in these substandard conditions, they saw us in the NYC 911 prehospital participating provider business enjoying great pay, benefits, working conditions, etc.
On top of that, FDNY more or less got along with EMS prior to the merger. For one, post merger, the engines became CFR, and now had to go on higher priority EMS jobs. The fire culture is that EMS are mutts, an inferior class of people, and don't deserve to have "FDNY" on their sleeve, as it's brings a bad image to the FDNY. The interesting thing is that FDNY doesn't have this attitude towards hospital EMS, just their own. We wctually got along well with fire.
What's more, NYC is one of many places that have become militant with quota hiring at the expense of merit, as in the most qualified for the job. One of the mechanisms created to advance the quota hiring agenda is the FDNY EMS to FF promotion. There are many more minorities in EMS than FDNY. If you "backdoor" your way onto the FDNY FF hiring list, you're given a number on the list that's above anyone on the competitive list. You're chosen first, above everyone else.
CA&O3 hit the nail on the head. As a FF you work a 24/72, have great benefits, a 20 yr retirement, a liveable wage, a better career ladder, no street posting, and you get to enjoy firehouse life. To boot, if you like EMS, you can still per diem at a hospital with all that time off. It's an apples to oranges promotion, but can be viewed as a promotion nonetheless.
Edit: I decided to promote myself and take the FF/medic positon in VA. I've got the best of both worlds, as I see it.
Two websites for reference and entertainmant:
http://www.afscme2507.org/
http://www.fdnyemswebsite.com/
Also, check on firehouse.com. There are several threads on the EMS to FF promotion. It'll explain a lot.