Has anyone ever heard or read why the 25-06 and .280 are the only ones offered in 26" barrel?
Until the 22-250 came along, the 25-06 was the most overbore cartridge they chambered for, and I think it needs the length.
I suspect the .280 has a 26" to differentiate it from the nearly identical .270.
The 35 Whelen was also a 26", I wondered if that was because the 35 Whelen was intended for serious shooters who would rather be able to cut a too long barrel than be stuck with one too short for their purposes, but I really don't think the barrel length is as critical to performance in the Whelen.
When they made 7x57 and 7x64 a couple of years ago, they came with 24" barrels.