Some of the lower-end scanners do have higher optical resolution, but still might not give you the best or the fastest scan. They might come with lesser bundles. Also, some of the more established pro scanners don't have to play the 'bigger' resolution game, especially if they've proven themselves over time.
It really depends on what you need, or, what the intended use is for. Resolution isn't everything - color fidelity, scanner driver, speed are just as important.
If you're planning on scanning 35mm negatives and slides, with the intent of using them in print, or printed at significantly larger sizes, then you really should look at a film scanner. You'll get better scans of your stuff than with a flatbed & a transparency adapter, unless you're planning on spending a lot of $$. Nikon's stuff is pretty good, and it really depends on how much you are willing to spend.
If you shoot primarily medium-format, you can get by with one of the more expensive flatbeds with a transparency adapter. I get pretty good scans on my medium-format chromes from the Epson 1680.
If you're talking about scanning photographs - not film - (it doesn't sound like you are) then you can probably get by with a cheaper flatbed, and then I'd go for the higher resolution. Just remember to check the maximum hardware resolution - that's the important number. The interpolated is like the digital zoom on a digital camera - rarely useful for pro work.
I'm sure others more knowledgeable than I will chime in, but I hope this helps a bit.
best,
Rick