I don't see how it would be impractical IRL - Or how massive a difference it makes!
It's not exactly the same as having left-mouse / right-mouse, but it's a split second to change from one colour to the other... It's not like you can fire two portals simulaneously anyway, is it?
Okay, lets put it this way. Imagine you are playing the game, let's say for PC -
As is, the left mouse is the blue portal, right mouse is the orange portal. This is a streamlined way of playing. You always know a left click is blue and a right click is orange, and because of this you can glide through the levels with ease. You can, in mid air, shoot one portal at a wall then another portal below you before hitting the pavement.
Now imagine if they changed the right mouse button to the "pick up" command, and made the left mouse a general fire button. To pick your portal color, you have to use the scroll on your mouse. You scroll up for blue, scroll down for orange. Now it is the same scenario, you are falling, you need to place two portals before you hit the ground. Only now, you have to scroll up or down on your mouse to change the color, and you have to keep track of what color you are set on, on top of what color you need to switch to next. Nobody would want to play like this. It would be tedious, and in 20 years we'd be seeing an episode of AVGN about Portal with the Nerd asking "WHAT WERE THEY THINKING?!?".
I am sure they did it to save money, fair enough, but check out the
Portal Gun light and sound kit from Crix; that's how it should be. I don't have the Crix kit, though mine is the same principle, and the in-hand function feels as smooth as it does in the game. It's as simple as moving your thumb from one portal button to the other, just as simple as moving your index finger from left mouse to right mouse.