I never said the P228 or the P226 came in .45. I said the H&K Mk23 SOCOM (or whatever it's called) comes in .45. I also never said that the SEALs didn't like the 9mm.
This article from Defense Review
actually has a pretty history on the adoption of the Beretta by the armed forces, including the adoption of the 9mm. The 9mm was selected by NATO as the standard caliber, so we, being sort of the "bosshoss" in NATO, decided it would be our standard caliber as well. You can look up the Joint Services Small Arms Program, and the XM9 trials if you'd like information on the selection of 9mm as the standard service cartridge.
The point that I am laboriously trying to make is that yes, the SEALs use the 9mm, because they are issued a 9mm. The "other" SEAL handgun, the H&K Mk 23 chambered in .45 ACP is a "special purposes" gun. 9mm is the standard cartridge for the DoD, so their gun is a 9mm.