2013 update: I've just bought a new load of these from my local hardware shop. I have always preferred these to brown (or other coloured) plugs, particularly for long screws or where a heavyweight item needs a secure fixing.
I don't see why the length is an objection - they take up relatively little space compared to the plugs on a sprue. Doesn't take much to keep them tidy cf. a box of loose plugs.
If you use the right drill size, they
don't rotate in the hole; they're very snug - I tap them home with a tack hammer. But they're not cheap unless you can buy in bulk, so I could see why professionals might avoid them.
Choiceful still have white, red, green and blue online in bundles of 25.
DP Tools don't appear to stock them any more.
Warrior Warehouses also have them, but you have to call them for delivery prices.
Amazon also have them, at pretty much retail prices.
Quite a few others too - just google "300mm wall plug".