Plus they do business all across the country; in the newer parks they seem to do a great job of incorporating local vendors (here in Philly they brought in a bunch of local craft brews, a few cheesesteak places - including Tony Luke's, best in the city, IMO - and
one of the best sandwiches ever).
This website is worth a look if you want to make yourself hungry.
ARAMARK Stadiums & Arenas