From my (limited) knowledge on the subject, yes, a sealed design (if all other factors are equal) will yield tighter bass as people call it. So what about all of the ported subs? Well, sound travels through a medium (air in this case) and the more air you can move, the more "bass" you can get. A port allows for more air movement.
You will also hear people "tuning" their subs for even lower frequencies by messing with port sizes/lengths. With a sealed box, it would seem that things are a little more limited.
I am probably 200% wrong, but that is what I used when I built a sub box for my car years ago. I wanted the tight bass and not massive bass (I wanted to add to the music, not dominate the music) so I went sealed.
Home theater, to me, is a different story, and I like ported better.
