That's undoubtedly true in general, but there are exceptions. For example:

It's a little hard to tell just looking at specifications without directly comparing in person, but I think the Costco Black Friday-specific version of the Roland FP-10 digital piano actually manages to be better than the normal version (even before you consider that it's cheaper and comes with a bunch of accessories). Specifically, it has 128 voice polyphony instead of the regular 96, and the only other difference I can find is that it advertises "a custom selection of tones curated by Roland and Costco exclusively for the FRP-2-ACR," which I hope doesn't mean they're worse.