In the grand scheme of things it IS a minor sport in terms of viewership.
Millions of people aren't flocking to their tv's to watch MLS soccer.
World Cup of soccer is generally going to garner higher ratings; just like Olympic Hockey did last year.
MLS (playoffs or regular season) won't have higher ratings than the World Series or the Stanley Cup Finals.
You're comparing apples and oranges.
In terms of viewership it is very close to hockey already, if not better.
Even discounting the world cup (yeah how convenient some try to pass off great ratings of 96 games over 13 months as just a curiosity and compare them with about 20 games related to the olympic circus every 4 years) here are some of the numbers soccer get in this country..
- Couple months ago the champions league final got over 4 mil viewers, a game involving two clubs from another continent. The 4 semi-final legs drew close to a mil on average despite 2 of them being on network available to only 40 mil household dragging down the average.
- Two weeks later, the Gold Cup drew great (similar to NHL early round playoff) ratings with the final getting over 8 mil viewers.
- Mexican league beats out NHL ratings (minus the last few SCF games) and that's just one group of soccer fans in the US.
- Many exhibition series invloving national teams and league clubs draw well on cable. World Football Challenge (involving some of the top Euro/Mexican clubs and MLS) that is being televised by ESPN is drawing much better than NHL regular season (not to mention 50-90,000 per game at the gate at an avg ticket price of over $60).
- Copa America, Copa Libertaores does better than NHL regular season.
- EPL gets nearly similar ratings to NHL regular season on versus despite the awful AM timeslot many of the games are on.
- MLS gets lower than NHL but not too bad given its expenditure level, lack of history and the internal competition is faces with other soccer leagues.
- Spanish la liga, German Bundesliga, Italian, Brazian Serie A, Argentine league all have their own fanbase here with small overlaps, tuning into their favorite soccer networks like FSC, FSES and GolTV regularly.
- Hundreds of thousands watch dozens of Euro leagues on broadband (ESPN3 and illegal sites) every week.
Also, lets not forget the hundreds of World Cup/Euro Cup qualifiers that also have decent to great ratings.
Soccer has the viewership .. just fragmented is all. There are so many leagues, tournaments, qualifiers and exhibitions going year-round on so many channels the fans have only so much time to catch more than a few. That's especially true for the casual fans. If soccer had only one big league with huge payroll, operating only 8 months a year and handful of games during the olympics every 4 years their numbers would be consolidated into a major level, visible to the 'naked eye'.