That Amsoil link references the infamous GM filter study filed with the SAE. I have debunked that myth several times. Excellent example of how uninformed people don't understand what they read. And to really understand what you're reading, you cannot use a marketing hype-filled sales promotion tool to glean real insight; you have to purchase and read the full SAE study! That study is worthless because in no way, shape or form does it represent anything remotely close to real world operating conditions. The test was GROSSLY biased, on purpose, to bring a condition to light that nevers happens in your average garage. It is completely useless to you, me and anyone who follows typical maintenance routines. Period. And I am more than willing to back up my claim with factual information directly from the study (I can reference specific facts, but cannot post large quotes or images as it is copyright protected; I do own a copy that I purchased some time back).
So, is filtration important? Yes, and no.
Yes - to a point. Most any decent equipment OEM is going to know what particulate loading and efficiency levels will sustain a long lifecycle of the equipment. Once those are established and followed, things will be fine.
No - past a point. Having "better" filtration (defined as substantially more finite) does not do a darn thing for the lifecycle of the equipment. There is not one SAE study (or other entitity for that matter) that shows conclusively a reduction in particulate size directly has statistical effect in longevity IN REAL WORLD CONDITIONS. This is because filtration is only one of three tools that help manage wear. The other two are more important, and contribute on a greater scale; those are the OCI duration and the tribochemical barrier on part surfaces (SAE study 2007-01-4133). It is completely erroneous to assume that only the filter matters. Essentially, once filtration is established at the required level, the benefit curve greatly drops off dramatically.
Where does "better" filtration benefit you? In oil lifecycle. Keeping the oil cleaner for a longer period of time can really pay off with extended OCIs. Superior filtration is a tool to manage the costs of the OCI. Whether it's a "better" full flow or bypass, anythying that keeps the oil clean for a longer period of time can be a benefit, if you allow the OCI to be sustained.
Once filtration is "good enough" for the engine, it is the wallet that benefits from "better" filtration, but ONLY if you use it long enough to pay off the investments. Your ROI is only as good as your ability to keep your hands off the wrenches!