Having organized shows in the NY/NJ/CT area for nearly 10 years, I find that hard to believe.
Most vendors attend shows because they're money-making events for them, and most that I know don't miss the opportunity to attend.
As for modelers, the same holds true. When I go to Replicon, (and I've gone every year since 1991, except for last year,) I meet and greet mostly folks from Long Island, CT, and even Mass. Most of the NJ guys that go, travel with us in a group.
When I go to Mosquitocon, I see some of the same Long Island faces, but far fewer. It's mostly a NJ crowd, with folks travelling from as far away as Virginia to attend the event.
Let's not instigate inter-club politics here, okay? Long Island is IPMS Region 1, and NJ is IPMS Region II. Technically, there doesn't need to be any date confirmations between regions that I'm aware of. Since I'm dear friends with the Region I coordinator, Doug Hamilton, and since he and the Region II coordinator, Tim Hortman, are quite active in the regions, we (NJIPMS) have always tried to make sure that shows weren't on top of one another, especially within our own regions but also within Regions 1 and 2.
But...when renting the PAL hall (and this was an issue when I was VP of NJIPMS), we found that our regularly scheduled date for the show (in March) was the same weekend as a basketball tournament. We'd had the conflict previous times, and it restricted the size of the show we had, and parking was nearly impossible. So we changed the date, and this was the one weekend we found that didn't conflict with the PAL's annual schedule, or the Region I or Region II schedules.
Jeff