What makes the most sense to me is this. Jean bart just joined Law's crew 2 years ago, we know Bepo is a big player in Law's crew, likely those other two guys in the spread are as well. It appears Law's crew is bigger than Luffy's (as most crews are). There isn't room for every member of Law's crew like the Strawhats so only his most prominent members got on the spread. Realistically, Jean bart probably just isn't important enough to make the cover.
You very well could be right. I like my idea though..
On a side note, I don't think Law's crew is bigger than the Straw Hats. It wasn't pre time-skip, and if it was now..Aside from Jean Bart (and the crew shown) I'm willing to bet they're all fodder, or at least used to fight fodder..
ā- Update From New Post Merge ---
Twice?
Yep, twice.
The first time was back when they were originally talking about the alliance and Chopper/Nami said they wanted to stay and help the kids. He assumed Luffy would go on ahead without them.