PhotoPost just came off a $99 sale last week. There are many features that PhotoPost has that other galleries do not, I would suggest you check out the Comprehensive list of PhotoPost features and compare.
As for features that PhotoPost has that vbg lacks; the list is long, but a few items would include: multi-paged indexes, announcements/category introductions, multi-category assignments for a single photo, cell phone/email uploads, gallery-style layout/portal style layout in addition to forum style layout, configurable placement of filmstrips (top, bottom, left, right), RSS feeds, sidebar configuations (including a new calendar layout, recent comments with thumbnails, etc), and a new advanced caching system that makes PhotoPost blazingly fast, etc..
For example: http://www.michaelpierce.com/gallery/index.php
These different layouts are simple switches and involve no custom modifications to the code. And, yes, PhotoPost uses the vBulletin style system so that when you change skins the colors on the PhotoPost side match your forums (you can even create new templates to match your custom skins). A good example of this is at: http://www.extremefitness.com/gallery/index.php
- although you need to be registered to change stylesheets - I have template sets for several of the extremepixels.com styles I purchased. http://www.viperalley.com/gallery/index.php
- (another example of an indexed gallery page) another unique feature which demonstrates our "contest" feature which allows a category to be tagged as being a contest which instead of rating images people can vote on (one vote per member). When the contest is ended, the photos are sorted by those with the most votes.
The IPS (Image Protection System) is unique to PhotoPost - you can store original sized images in a password protected area (or even outside your web directory) and force users to use PhotoPost to view any images - if you don't have permission to view an image, you won't be able to get to it. With vBgallery (or any other gallery), if you know the URL to an image, you'll be able to share that image link with anyone and bypass any security the system has in place.
PhotoPost has been integrated with vBulletin (and others) for many years, has a history of innovate new features and a dedicated support staff. In fact, the upgrade for 3.5 users is painless because PhotoPost doesn't require an upgrade or reinstall, it automatically senses the new version and compensates immediately.
I always recommend potential customers do their homework - if we can be of further assistance, just ask.