Presumably they'd not like 4e even if pathfinder existed. The only people that pathfinder steals are the ones that decide they don't like 4e because pathfinder came out.
I think you are underestimating the "shininess" effect, especially among GMs. While there are certainly those that have been playing with their same original 1E PHBs and DMGs, I think most GMs like having new stuff. They LIKE spending their money, because gaming -- specifically, D&D gaming -- is their hobby, and people spend money on their hobbies. This creates a powerful internal motivation to adopt the new edition of a favorite game. I love old school D&D, for example, but the retroclones have allowed me to spend money on shiny new D&D stuff, and this pleases me.
But Pathfinder isn't a retro-clone. it is "current D&D" competing directly with official D&D, simply because it exists. Many of those people that don't like 4E may well have stuck with it if it was the only currently published and supported D&D, but because of Pathfinder it isn't. That means that the GM can get their "shiny" fix and not have to conform to a kind of D&D they don't like.
I think it is important to differentiate Pathfinder from the FantasyCrafts and True20s and even Conans. While those are all great fantasy games based on the OGL, none of them are D&D in the way that Pathfinder is. D&D 3.x lasted nearly 10 years. That is a lot of time to build a dedicated following and create a whole generation of D&D players who, like the old school and my own "middle school", identify D&D as this particular kind of play and game -- plus convert and hold a bunch of earlier fans.
Certainly more players moved on to 4E than switched to Pathfinder, but I don't think anyone is claiming that Pathfinder is bigger than 4E. Rather, I think the suggestion is that Pathfinder is *significant* in a way that no other OGL fantasy game is (I say it that way because I think M&M is a truly significant OGL game, but that's a different issue) and its success is going to impact 4E. Those pointing out the "grognardization" of Essentials are spot on.
And here's one last anecdote: I run Pathfinder because the people I play with had absolutely no interest in 4E and preferred to stay with 3.5. I lobbied for Pathfinder because I wanted the shiny, as well as wanted a few "fixes" to 3.5. These guys have been playing D&D since 1981 or so. To them, Pathfinder *is* D&D now, and 4E might as well not exist at all. What's more is that we have introduced one new player via 3.5/Pathfinder in the 4E era, and one player and myself both have kids just about to make their first forays into gaming -- and we're not going to tell the kids that they can finally play Pathfinder with us grown ups; we're going to tell the kids they can finally play D&D with us and we're going to do so via Pathfinder.