the pants make a huge difference they're uggeg, have patting and strategic pockets.
Jerseys though, I'm not really sure. I bought one cuz it was just as cheap as getting a new longsleeve shirt that I grew out of. Some of them have grip where you old your tank and a little padding on the arms as well.
obviously a team will wear them for identity pruposes.
Also, jerseys are elastic. So you can move better in them. Also, they are easier to clean hits off of. If you wear a shirt, it will leave obvious paint stains all day. Whereas in my experience, with a jersey you can usually wipe it off and not blatantly tell you were shot earlier.
I wear my paintball pants as well as a jersey (when I get one) for mainly comfort. They are padded, extremely breathable, and also fashionable. I'd rather spend the money to be cooled off, protected, as well as decent looking while playing rather than be sweating, hurting, and look like I'm trying to make a fashion statement!!
I know a guy that has a jersey, and yeah, he just wears it because he thinks it's cool. Obviously if you have a team you wear it so it represents your team, so I think this is more about why would you otherwise.
But I took a quick look in it and I can see where the "bounces more" comes in - the jersey's 1.5cm thick with padding.
If you get a good jersey (08+) from any major brand they have padding where you're most likely to get hit. If you get a chest protector (like Empire or Proto), they can make balls bounce to and make the sport a little less painful. Paintball Jerseys also clean off much better then a cotton T-Shirt or BDUs...so if you want to wipe its that much easier. If you get an older jersey, the only real perk is that it makes you look like you play Tournaments.
Pants are awesome. If you crawl, crouch, or slide at all these make the game so much easier. Instead of scraping your knees, and hitting them on rocks you have a long thick portion of padding to protect your knees. You can say, "isn't that what knee pads are for"? Knee pads serve that purpose but I find it much easier to run without knee pads restricting my movement. You also get a lot more bounces off of the pants.
The pants are important for many reasons easy to clean, padding, pockets etc as said above as for the jersey mostly I wear mine so our team is uniform the same reason all teams wear jerseys for the uniformity. Additionally my jersey has some padding on the elbows and shoulders for a little more protection and also has some grip for the tank.