Well as I recall everyone and their mother complained that Scotland was not even included as a minor faction in MTW1. Add to the mix the number of modders who addressed the issue by making Scotland playable and the fact that CA eventually made the Scots into a playable faction in Viking Invasion and you can why CA decided to make them a playable faction in MTW2.

I get the feeling there are more Orgahs dismayed about the inclusion of the Aztecs at the expense of some other European or Asian faction of historical note (i.e. Aragon) than there are people disappointed about the inclusion of Scotland.

I really look forward to playing as Scotland for the same reasons as I enjoyed playing the minor factions in RTW (i.e. Armenia); it's incredibly fun to play a faction with its back against the wall and the odds stacked heavily against it.