Glad I didn't see that other trailer before, as it spoils the reveal of Knowhere and some of Groot's abilities. The first teaser with all the prison introductions to our heroes works much better without giving away too much.
I suspect there were supposed to be more songs on the actual mixtape than we would have heard in the movie.
That is a pretty interesting theory, doubleofive. Maybe you can ask Gunn on his Twitter?