Both can be attributed to them just not wanting to show all their cards in the first trailer, especially the Sky Rail thing, since they kept Shadow intentionally mysterious and hidden in the marketing for quite a while. The only real evidence for it is that 1) they weren't shown in the first trailer and 2) there's early footage of Sonic in Sky Rail instead of Shadow. Honestly, I've never bought the whole 'Tails/Rouge/Shadow weren't originally planned to be playable' stuff.
