I think I have to speak up for Microsoft Poland. Most companies like to pretend the local market matters, and therefore that any commercials and promo material was made locally, tailored to the specifics of the market. To show that they "care" for the [insert country here] users, "really, they do". Of course, they don't really make all their commercials locally, but they do edit their material to apply to the local market instead of screaming "MADE WITH PRIDE IN AMERICA, NOT HERE." In this case, they wanted the ad to show the staff of an average Polish firm, that the customer can identify with. And with less than 1% black people in the population of Poland (most of which are in college and not native Poles, and don't plan on staying), that old black guy is anything but average. In fact, he'd stand out more than the white head badly photoshopped at a weird unnatural angle on a body with suspiciously dark hands. Redoing the campaign set would have been more expensive, although in hindsight it would have saved them a lot of bother.
tl;dr: it's not racism.