Yes, they are absolutely good for gamers and industry. In a narrow view analysis it is bad because you need to have all system to enjoy a gen, but on the wider one you get more gems because each company needs to win over the competition.
I will elaborate, in fact, I was thinking in making a threat like this:
I will use Halo as example, it was a big hitter and put the new arrival, Xbox, in the mouths of many gamers. To compete with this Nintendo and Sony needed to get their own "mature" FPS on their console, making/allowing/give more resources to their own exclusive FPS: Metroid Prime and Killzone (mainly). Yes the PS2 has other (better) FPS like Battlefield 2 or Black, but they where not exclusive and could be also played on the Xbox; and Nintendo is just Nintendo, they could just say "people will still buy Mario". I want to focus on Killzone, anyone that played it knows it is a really "meh" game, not bad, but it was not good either. In other words, I doubt many people bought a PS2 so they could play Killzone. This is to say, it didnt deserve a sequel, but Sony needed an FPS, specially now that Halo and Halo 2 where a success and that the 360 will definitely had a Halo 3. So they pressed on, give resources and the spotlight to Killzone 2... and this game is really REALLY good, a thing that probably wouldnt exists if it werent because Sony needed something against Halo.
This can go beyond ofc: platformers, simulators, etc. But the point still stands: Yes it sucks that in order to get all the good FPS you needed to get an Xbox, a PlayStation 2 and a Gamecube. In a world without exclusives chances are that yeah, you could play Halo on all paltforms, but you would not have (or have a very poor quality) Metroid Prime or Killzone. I mean, why would they give more resources otherwise? if CoD would be exclusive for the Xbox/PC Sony would have to get their own FPS, maybe even resurrect Killzone.
And speaking of money, companies will invest on these games, even if they barely break even, but because those games will get systems sold.