Pro Tools (and any other decent hardware/software DAW combination) does more than just record . The real magic is in the breakout box/audio interface you probably would get protools with – it has a fairly decent analog-to-digital converter, at least one XLR input (try finding that on your regular sound card) and a 1/4 inch direct input jack, that does level matching and other things to avoid feedback and clipping.
It also tends to support shiny things like ASIO (letting you use other non Pro Tools software that supports it with the audio interface).
Even with vocals, there's a big difference between a mic attached to your computer input, and a mic (granted, a better one) connected to a Digital Audio Workstation (Pro Tools is one, there's also Cubase or Apple Logic among the most famous ones). It's a lot clearer, and with less noise.
In addition, you can use software to mix the recorded music.
It's a little like comparing a station wagon to a proper truck – sure you can load a lot into the back of the station wagon, but when you need to move a piano, you want the truck.