People do it but there is no real reason you need to bed the first two inches of barrel when glass bedding a rifle with a typical sporter weight or typical factory bull barrel.
If, on the other hand, you are to build a rifle with an exceptionally long and heavy barrel it helps to bed the entire length of the barrel to help support the barrel and remove stresses that that heavy barrel will put on to the receiver.
If you want to know the truth... When you fire a cartridge the chamber area expands radially. By bedding under the chamber area of a rifle you are actually not allowing the chamber area to expand evenly around the full 360* of the barrel. What you are actually creating is uneven radial chamber expansion. If the barrel is completely floated all the way to the recoil lug the barrel expands evenly all around the circumference of the barrel.