In the design world, many times the people making up the ads will use what they have available to pull from to get things like screen shots. This designer probably had an iPhone and needed to show something on screen so grabbed a screen shot of the Google Maps assuming it would look similar enough on the Droid X.
It's the same reason why many catalogs show Macs on computer desks instead of PCs - aside from the obvious aesthetic improvement, of course - or show OS X screens on PC laptops.
I always get a chuckle when I see that, especially since most people would pay no attention to the discrepancy.
Chances are the person making the ad has an iPhone. Hell they might of quickly pulled up google maps on the iPhone took a screen shot then put imported it into the ad.