From what I've read of Matheson, his style was very mid-20th century, particularly mid-20th century sf/f/h. There was a belief expressed by some sf writers that prose should be as transparent as possible, which led to writing that was nearly journalistic. Against this mindset, there was Bradbury, Sturgeon to an extent, Pangborn to an extent, and Cordwainer Smith, with only Bradbury really developing a wide readership, though I don't think even the writers who professed the belief were always representative of it. Later writers in the '60s pretty much thumbed their collective nose at the belief (Ellison, Moorcock, Le Guin, etc.)
I think if you look at genre writing from the 1920s on, there was greater and greater influence from the Hemingways and Hammetts and those influenced by them, all of whom pared down their prose and believed in the "less is more" credo. Matheson is certainly pared to the bone and later writers like King in some of his best work and, maybe, Dennis Etchison did much the same, often to great effect.
Still, as you imply, there's a element of subjectivity involved, too. I grew up reading noir, hard-boiled, mid-20th century writing, so I'm used to it so while certain words and phrases may seem dated to me, the prose style doesn't strike me as out-dated. (Which, it occurs to me, might say something about my out-datedness.)
Randy M.
(Oops. Meant to add, yes, a lot of the ideas that Matheson put forward have either been dramatized directly or cribbed and reworked by later writers like King.)