I can't give you a reason other than speculation. The author of the blog post states that he had to go to Google cache to find the page in the first place, so there's no telling how long ago it was removed from Mobiquity's site.

It makes no sense for them to remove the entire page when they could simply replace the Starbucks logo with that of another clients. Couple that with the fact that we have no idea when the page was changed and it sounds more like removing the client page was part of a decision regarding the overall content of their site and not an attempt to hide anything.

A past affiliation between Starbucks and Mobiquity has no bearing at all on the current situation if it is not ongoing, and still doesn't imply any personal affiliation with Mr. Stark.