Well, Semogue has Best, Super, Extra, Premium, and Special grades, in addition to other specialty grades used in limited-edition brushes.
Best, Super, Extra, Premium, and Special grades are all listed right there on the wiki page. Banded imitation's not a grade, it just means they're dyed with a band to look like badger. Omega doesn't really list their grades, but that doesn't mean they don't have a range of grades used for their different brushes (they certainly do), and just because other companies only have 2 grades doesn't prove there's no variation in boar, especially since Semogue is what Steve was asking about.
There are backbone/floppiness "issues" because different brushes have different strengths. A brush that is excellent for one use (such as the 2000 for being big, luxurious, soft, and excellent for bowl lathering) might be terrible for another use (such as face lathering). These aren't "issues" with Semogue brushes, they're just people trying to find their ideal brush, which is only possible because there's such a big range. The ability to fine-tune your selection to match your individual preference shouldn't be looked at as a downside.
The idea that grade means nothing and it's only tops that matters is kind of silly, but it seems like you're not the only one to get that impression. It would be like saying there's no difference between Pure and Silvertip badger, that only bulb/fan shape or loft mattered.
I think the biggest reason boar is thought of as lesser and having less variation for aficionados is because boar bristle is not rare and expensive like badger hair is, so the brushes are cheaper. Many, myself included, greatly prefer boar over badger. I'd rather have a $30 Semogue boar brush than a $200 Simpson badger.
Thanks. That chart is helpful.Here's scoppi's great effort to list the popular Semogue brushes:
http://badgerandblade.com/vb/showthread.php/278205-Semogue-Boar-Brush-Chart