You're both right, mostly.
Race-grade carbon-fiber (not fiberglass, but same idea) bicycle frames have integrated seat masts with adjustable height mast caps. So, most of the seat tube is integral to the frame, requriring that the frame be roughly the right size for the rider. The seat cap's height is adjustable to set the last few mm's of height to exactly what the riders preference is. It's a great system, as you get all of the benefit of an integrated seat mast (added strength and reduced weight at the top tube/seat tube/seat stay junction, reduced weight because you don't need a clamping system for the seatpost, reduced weight from not having a seatpost, some vibration reduction from the extra carbon) without the steep penality of having to make an absolutely custom sized frame for each rider.
They are, generally the same bikes that you can get from a high-end bike shop. Occassionally they'll use an in-development carbon for the true pro frames to see how it holds up (Trek did this with the 110(?) OCLV frames before they brought them on the market, IIRC), but otherwise, they're the same.