I've had sky and virgin too.Though I found both expensive ,sky edged things on the tv front and virgin were better on the broadband front so you may just have a point. You might lose out on their package deals though and pay higher prices. FYI I'm currently with talktalk for broadband & phone & freeview plus.
I'm no friend of Sky for reasons too numerous to go into in this thread but it seems to me if you've already paid blood-money for a Sky TV subscription then it makes sense to take advantage of their low-cost phone+broadband package as well?