Initially, the burden of proof is on the homeowner. They have the freedom to show you the windows and allege wind and barometric pressure.
Then, the burden of proof shifts back to you if you are going to deny the claim. Now, you must prove that it's not wind. You can not deny a claim because you happen to disagree- or because you found a seemingly flawless answer on an internet forum...
As an adjuster, you can do a reasonable job of inspecting the cause of these failures that can serve as basis of a reasonable denial; inspect all elevations, consider wind speed, barometric pressure changes, research the brands to identify recalls. On a flat rate billing arrangement, I realize this can be a very scary proposition for some. I know, who want's to work for free?
The seal failure of windows is not something that can be addressed with a broad stroke or an engineer report such as the one Ray spoke of. I'm sure it would be a nice read regarding the failure of numerous installations. This would serve as a decent bulletin to teach adjusters/investigators additional points to consider. Nice fellow, I just disagree. Alone, this would not serve as a reasonable basis for denial- just bad faith fodder.
All claims are handled on an individual case by case basis. Just because an insurer did something one way, doesn't mean you assume that you should too. Accepting consensus in the place of a proper investigation is a very bad way to go. In my recent experience, it was cheaper for the carrier to pay for the windows (less than $1,000) than to hire an engineer for $1,500 to $2,500 to dispute the precise cause of the failure. I was told to pay, so I did.