The may be true of some packs, but certainly not all. Boots can't be adjusted to fit your foot, but good pack systems can be adjusted (in many ways) to fit different shapes, sizes, and body types. Many boots either work, or they don't. But if you look at our packs as an example, we have multiple frame heights, micro-adjust torso settings, micro-adjust hipbelts, lumbar shim system, and more option to dial-in fit for YOU. We sell only online and have an incredibly low return rate, so it can be possible to buy a pack "sight unseen" and have great fit. (We also offer a 30-Day trial period, so that you can ensure the pack will work for you.)
I'm not saying that as a sales pitch for Exo, but to bring to light some of the things that guys looking at packs online (from any brand) should consider in terms of fit/adjustment.