cangreylegend,
Saab went thru the same thing quite a few years ago. They used to fit the larger ACDelco PF13s & Mann W920/26s, but when newer models with smaller working spaces were introduced they needed a filter with a smaller OD. The new, smaller filter (PF53 & W712/38) had the same gasket diameter & bypass pressure rating, so it could be easily retro-fit onto the older models. As the Dali Racing Guy says, the new filter was deemed "sufficient" for the needs of all the cars, regardless of previous applications or current fit limitations. The benefit for Saab, obviously, was only stocking a single filter for the different models.
All car manufacturers have "classes" of cars; everything from Basic/Entry models to Premium models. Saab changes things like intercoolers & exhaust systems on otherwise comparable vehicles to create some of the differences. With Acura, my impression is that the "super-premium" filter is being used (along with other, less subtle stuff) to separate the NSX as being "a step above" the other models. (I mean, really, how would it look if your Super Car used the same peripheral parts as your Base Commuter Vehicle?)
I don't agree with the Dali Racing Guy's comments about bypass relief valves, however. While, theoretically, having the bypass valve at the base of the filter is preferrable, there are numerous examples of manufacturers spec'ing filters for decades with the valve at the other end of the can. Some manufacturers even spec filters which don't have any valve, preferring instead to control it in the engine's oil plumbing. If a filter goes into bypass, that doesn't mean there is no protection (as the DRG suggests). It only means filtering has been temporarily bypassed in order to continue providing protection (the oil bypasses the filter media to ensure it still gets to the engine!). And while I agree that you don't want to stray too far from the manufacturer's specs, I think any high quality filter designated for your car would fall within the deignated bypass tolerances. Flow vs filtration has been an on-going debate here for months, with equally fervent believers on both sides of the issue. Check out the five pages of posts on Bob's Filter Tests for just a sampling of the viewpoints!
