I hate to Burst your bubble, but Magical kingdom Express and the Yellow Mears buses are one in the same. Disney doesn't own any buses. their entire fleet of buses including their downtown Disney transit public buses are all own by Mears LLC. Mears has a monopoly on all commercial traffic coming in and out of Disney resorts. Except for groups who charter their own out of town Buses all the buses you do see even the non Mears ones are sub leases by Mears to operate on Disney Property. Reason for this is the business law of limited liability. Disney can not afford to be liable for transportation and adversely effect it's bottom line with resort and amusement park revenue. That said Mears has a duty to keep the amount of traffic incidents down are Disney will be force to dump them like a case of rotten eggs.