Actually, when you shop for an upper at RedXarms, they state "THIS UPPER IS DPMS COMPATABLE". When you shop for an upper at Hardenedarms, they state "Fits DPMS style lower receivers". When you shop at MidwayUSA, it's "DPMS LR-308". You can be right about the SR-25 pattern, but that's not what all the retails are using to identify their products.
I've never shopped at RedXarms, nor Hardenedarms, and at this far into my shooting journey, if I'm getting by just fine, I likely won't ever be perusing their wares. The reason you see references to "DPMS pattern" is because the majority of people can not conceive spending $1k on a firearm, let alone 2.5-3.2K for something like the LMT or LaRue rifles, and especially not the 4-5k for something bearing the SR-25 badge.
People relate to what they know, or what they
think they know. In order to make money in sales, you need marketing that speaks on the buyer's level. Sadly,the more people toss around "DPMS pattern" the more we'll continue to see this.
Fact is, "DPMS pattern" itself is all over the board. They have had rifles with different rail heights and now you have the Gen. 2 rifles. Which one is the true "DPMS standard?"
Dpms and sr-25 are different patterns. Manufacturers are referring to the magwell not the receiver pattern.
That's quite confusing. DPMS did not invent the magazine specs either, they used the SR25 specs for the mag well and mag bodies. They decided to go their own way with the receiver cuts. As such, it seems that describing anything as "DPMS spec" does more to confuse the issue than to help answer questions of compatibility, but I digress...
I have to agree, buy your upper and lower from the same company. Regardless of who started first, the fact is, no two companies are doing it the same.
The weird thing about all of this is that you can mix and match uppers and lowers from the SR25, MWS, LaRue, and Armalite rifles and everything mates up just fine. Now, granted, the legacy Armalite upper presents challenges that won't allow it to feed from the standard SR25 mags. The DPMS rifles, on the other hand, have a rounded profile like that of a regular AR15, so while they will fit on other lowers, there is an awkward gap whose functional integrity I'm not sure of.
At the end of the day, I agree to keep these projects as much of a single-source proposition as possible. It helps avoid major headaches and potential money pits. The big problem with PSA is there appears to be instances when even PSA components are not playing nicely with their kinfolk.
For the sake of long term sustainability, I think it wise to take note of what the Military has invested in. Of course, decades from now this too came become a concern; just take a look at the diminishing availability of M14 USGI parts as a potential example.