Agonz.... If you would have been reading properly, you would have noticed that the person who made the inquiry about the Pioneers wasn't the person who said they have the Jensen speakers.
Also, some people don't have $$$ to invest in higher end products. And, they certainly don't have the room to invest 3-4 cu' of their rear area to build an enclosure in.
As far as the Jensen or Pioneer speakers go. As long as you are not trying to compete or having anything that will give you "street cred", you will be fine with a simple 300 watt setup (150 per woofer) for 2 twelves.
Honestly, a friend of mine had two old Kicker Comps with 300 watts in a 2 cu' per woofer and it was pretty incredible. I mean the guy owned a SoundAdvice store, so he knew what he was doing, but for only 300 watts it was a good setup. More than enough when riding around town.