Organised fan groups have sprung up at clubs across North America in recent years, adopting colorful styles of support more familiar to European or South American football than the NFL or NBA.
"We are beginning to see a real evolution of the soccer fan in our country," Garber told reporters ahead of Sunday's MLS Cup final.
"For many, many years, people said, 'Hey, soccer is never going to make it because Americans don't understand the game, it's a foreign sport, people might play the game but they stop playing as teenagers.'
"We have proven in many, many markets, we've proven it in Toronto, we've proven it in Seattle, in Chicago and Colombus, that all of these people who have grown up with the game now can get into stands and can replicate that aspect of the game that gets them very excited when they are watching the EPL (English Premier League) or La Liga on television," he added.
"We now have that in MLS. To me this is a by-product of the league being around for 14 years, of expansion and more and more teams, very broad television coverage and deeper commitment to the sport (on television)...
"I think this is one of the most important developments in our league and something we are going to get more focused on. We listen to these guys and women and they are an important part of driving our thinking and our decision-making," he added.
The Seattle Sounders, in their first season in MLS, averaged crowds of over 30,000 while the league-wide average for the regular season was 16,037.
Garber confirmed that the league's aim was to grow to 20 teams in the current phase of expansion.
The Philadelphia Union will join the league next season with Vancouver and Portland to come on board in 2011, expanding MLS to 18.
"We know we are going to have 18 teams in 2011. We have had productive conversations with Montreal to be our 19th team, we have not put a timetable as to when that team would join the league if we are able to reach an agreement with them.
"We do not have any active discussions going on, of note, for a 20th team and we certainly don't have any timetable for the 20th team," he added.
Garber said he was "very confident" that negotiations on a new collective bargaining agreement would bring a result before the current deal expires in January and said talk about a possible strike by players was "totally premature" and "counterproductive."
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