The big difference is that VandeBerg was a more versatile recruit. VandeBerg projected well as BOTH a wide receiver and a ball-hawking defensive back (likely a free-safety). He had one season where he nabbed 9 interceptions. In his final 3 seasons in high school, he nabbed 21 interceptions! That is impressive! Furthermore, while many seem to think that VandeBerg is slow ... in high school he was listed as clocking a 4.4 40. I wouldn't overemphasize that time since I would venture to guess that it was hand-timed. But the fact remains that he's proven more than "fast enough."
Anyhow, all our speculation is a moot point because Martin now has many excellent offers ... and Iowa is among the group of schools he will choose from.
It will be interesting to see how Iowa's WR recruiting ends up playing out.
There is no comparison between Oliver and Vandeberg at this age. Martin is a well put together kid who's turning into an elite WR prospect.