Yeah I doubt it is 28/20, probably more like 28/23. My wife has one of those digital food scales, so I brought it to Dicks and weighed all of the different USA bats after I got one online that was way off. All of the -10s were really -6 or -7, and the -8s were -5 or -6. The disparity is heightened by the shorter bats, as I don't think they can get the weight down with the compact length. Once you get over 30" then they seem to start to get more accurate; but yeah the 28s are just boldfaced lies. The people at Dicks got so pissed of me weighing their bats and yelling "Fraud!" with each one that they gave me $50 off to get the hell out.
And like DeaconBlue said, the balance is a huge factor as well. Dicks has the Easton 750C that looks like it should be decent, but is so damn end-weighted that only the token team fat kid can swing it effectively. Which one did you buy? After weighing, buying, and returning probably 7 bats, We finally settled on the DiMarini Voodoo 2-piece 28/18, which is actually 28/20.5. It seemed to be the most balanced and lightest, but of course is $250 unless you load up on coupons. It hits really well on the sweet spot, but anything even partially off center is straight into the ground or straight up in the air.
The one I actually like the most is the $99 Easton 750 (not the C, but the white/blue one)... the 28 and 29 are way off on weight and the shapes are weird so not great for smaller kids, but once you hit the 30" it is relatively accurate and normal. This early in the season, the kids with those seem to be driving the ball the best from what I've seen BUT there are more strikeouts from kids who normally wouldn't using them because of the overall increased weight.