Highly regulated industries, industries with network effects, or industries that require very rare natural resources (diamond mines) are exceptions. See http://en.wikipedia.org/wiki/Natural_monopoly
you may have opportunities when the market is new, or when you create the "market" yourself.. but with time monopolies will take control and no more inovations allowed.. until of course.. someone innovates aside of the system and a new cycle begins.. but the old status quo are still there trying to demolish the new wave that is a threat to its dominance..
i could quote a lot of cases here based on reality.. but anyone can find several examples of that just thinking a little bit..
But in 10/20 years.. it will have 2 or 3 players at most.. so maybe a new cycle will happen again.. in other scenarios.. that may or may not will break this monopoly down to pieces.. but its visible that it all tends to monopolies.. i was not questioning were innovation was impossible.. or small players could start a new game.. but a small player cant enter in a old game and spect to win because the big players will crush him, or in the best of the scenarios will buy him.. (waze being bought by google to nail the competition of google maps)..
did'nt meant to be rude, ok?! sorry ;)
On the other side, those companies put large sums of money to "innovate" on the markets they already dominate, or in research to make them better in what they already do.. (so it doesnt really get into a innovation cicle)