Actually, team drivers race primarily with products that ARE available to the public. Yes they do testing of new products and whatnot, but who's to say they are better? Different does not mean better.
The only real advantage I can think of is getting the absolute best batteries. You won't find many (true) 1.170 or 1.180 (@30A) batteries at the retail level.
Still, if you give Pavidis, Lemieux, Cyrul or whoever your mediocre batteries and you run their true team packs, I'm guess you'll still get your ass handed to you on a silver platter. They need those extra little bits because of (what tc3screamin said) they are racing against other guys as good as they are, where every hundredth-second of a lap matters. When you, or I, or anybody else reaches that level, then we'll have access to that same stuff.
The other equipment: kits, tires, motors and so on, is the same stuff you buy at your hobby store. Sure there will be a prototype part here and there, but remember, for every prototype that works out and makes it to production, there were probably 10 others that failed. Thus when you buy something at the shop, you know you're getting the best stuff out there -- team driven and team proven (note: this may not apply to HPI. haha).
And on the rules: the ROAR motor rules are NOT there to hamper performance or to give team drivers an advantage. They are there because without those rules, teching motors would be nearly impossible. If you could legally mix cans and arms from GM3s, P2Ks, MVPs, Rage and so on, how do you tech the stuff? I would not fault a race director for not being able to spot the difference between each arm and can. You have to have rules in this area to protect the sanctity of the events, or else just say "anything goes" and be done with it. I prefer having rules.