Nope, purchased Quicktime Pro 7 about an hour ago, copied and pasted the license key from the purchase receipt into the Quicktime Registration pane, typed my name into the top line and hit tab and the Buy Now button disappeared.
Maybe you are not Tabbing from one field to the next in the registration pane.
Like this: Type in your name in the first blank, TAB to the next blank and enter your organization/business name if you want and/or hit TAB to the next blank where you will enter (copy n paste) your Quicktime Pro 7 registration key, hit TAB one more time and if the key is correct the Buy Now button will disappear.