As Overwatch said, if they are over 500fps, they are considered a firearm. In fact, anything over 500 fps is considered a firearm. A cousin of mine registered his homemade potato gun to see if they would, and alas, they did.
Most pellet rifles will advertise as shooting 495 fps, but most of them will hit over 600 without a hitch.
For the 1450fps rifles, they are pretty deadly, have it in .22 caliber (whics some are) and you have a reasonably quiet rifle good for 40 yards or so, semi comparable to a .22lr, mind you the drop off after that is fast and significant.
The only issue I have is the selling of BB pistols to gang bangers who actually use them to strike fear in some civvies.
For the training value to the younger kids (heck, i still shoot with a pellet gun once in a while, gives me the basics of pistol such as getting the right sight picture and trigger pull basics, and i get to fire in a small storage room inside my own house) i think that they are indispensible in teaching the basics in firearms safety and usage.
Too much government control, not enough common sense. Legislation does not correct lack of common sense on the part of the populace.