Over here in the US the feeds are coming directly from the Premier League with default english commentators in position for the standard games which air on the separate channels to maintain the coverage of all games.
When it comes to the games that NBC has picked specifically for coverage on NBC Sports etc then they have the english based NBC Sports coverage commentators; Arlo White, Graeme Le Saux, Lee Dixon etc. which then tie back to the NBC Sports studio in CT with Rebecca Lowe, Ekoku and Mustoe.
In the case of Lee Dixon and Graeme Le Saux etc they must have secondary contracts to work with other broadcasters. Much like Lineker who fronts the BBC coverage primarily but then does work on the side for NBC Sports and one of the middle east stations.
Seeing the financial details hinting at the 1BN that NBC Sports has paid for the next contract. It was inevitable that they paid more with the great job they are doing. Better, quality coverage which improves the brand will only lead to the Premier League charging more and more.
They do an amazing job here with their coverage, also helped by the time difference which means their is little sports competition on Saturday/Sunday mornings.
I think it all started when the guy in charge of NBC Sports was traveling through NYC and noticed the amount of people wearing club colors that convinced him there was something to pursue which got them their first deal.