I think the assumption of perfect competition is probably one of the biggest misconceptions of modern economics - people, even politicians - are so quick to talk about supply and demand, about market forces instantly reacting to weaknesses - but they never qualify that by discussing the competitiveness of the market.
Perfect competition exists only in theory - in practice - all markets have imperfect competition of varying degrees. ISPs in almost every country are oligopolies - meaning that common economic principles like supply and demand, or market forces do not apply.