If you click on that caption on The Peony Shop's home page it'll take you to a YouTube interview where they discuss their seedling program. They are very specifically talking about their hybridization efforts rather than the general propagation of named varieties.
I've talked to Joshua before and can confirm what Anya says, he says their main stock and even the propagations from their seedlings when commercially produced are traditional divisions.
As for TC's, the size we buy them at is probably equivalent to 1-2 eye divisions and they grow at the same rate as far as I can see. I've had a few purchased as around quart sized plants that bloomed first spring. The only difference I've really noticed is TCs have been harder to divide the first few times, the crown seems to be heavier and woodier. Can't tell the difference otherwise.
Anyone who has any of Don Smith's Itohs has a plant that has been tissue cultured. He told me himself during convention that he is a big believer in the efficacy of TC and that it's used to build the initial supply of plants for all of his intros. Divisions a few generations from initial stock is indistinguishable from any other root division as far as I can tell.
