There could be several reasons for this service operating in/out of YEG
as compared to YXD
1) A similar service using YXD
already operates, although using turboprop aircraft. That being said, there would be no issues with aircraft performance, or restrictions to passenger loads, operating a Lear 45 to/from YXD
2) Using FBO's instead of the terminals will save alot of time and will make this a more desireable option compared to simply driving the extra 2.5 hours.
3) As Wolsingjet and Flyb have alluded to, the imminent opening of the western Henday extension, and the opening of the eastern extension next year, will make accessing the western and eastern areas of the metro area almost as quick from YEG
4) Most of the "premium" type of passengers living in Edmonton who will use such a service already live in Southwest Edmonton.
5) Edmonton's corporate offices are not all based in the downtown core. In fact, there are probably more of them in the suburbs as compared to downtown.