Given the breadth of bikes and likely consumers a manufacturer like Giant has, versus say Transition (and therefore, likely competence and mechanical sympathy) you’d reasonably suggest that the bigger, broader brands might need at least two warranty policies depending on the product.
Equally, given the warranty applies to everything from suspension and wheels to frames, you could imagine why the the conditions and terms for accepting a warranty claim on a serviceable item like a set of forks or wheels could/should be much more restrictive than a frame.
One warranty policy to cover all clearly is flawed, which means really you’re relying (as are the manufacturer) on your dealer to support your claim where appropriate, and not submit claims where obviously not valid…
I’d have thought at the very least, you’d have been asked or thought to leave the seat post in when you dropped it off, it’s the only component likely to validate the claim. Hard to point your finger at the shop without knowing full circumstances, or the capability of the one person you spoke to, but I think that’s where I’d point my frustration – they should have told you stripping it yourself would likely invalidate the claim.
I can’t imagine the warranty terms for any of the big brands are much different – does anybody know?