Yes you're probably right.
For me, there is a difference between seasoning and stains - of course I would expect that the pieces would develop a certain used character which is very welcome: changes of color, micro-cracks showing more obviously etc.
But the thing is that mine has these 'macro'cracks on the inside and I was afraid that powder rests would get stuck inside them and be hard to remove - that would not be welcome, you see?
But you're right - they're made for matcha so its probably a good idea to trust the Japanese to have gotten the things right
Still, I'm curious about his (her) photos for an entirely unglazed Chawan.