That was never in doubt, I say "claim" because it doesn't seem like a good enough reason to exclude the slippers, in an attempt to distance his new film from the "original" (there was a silent era Wizard of Oz wasn't there?) if he's going to film the first 20 minutes in black and white.
"I don't want to" is a good reason.
"I don't want to because they weren't in the book" is less good.
I think the restrictions on referencing the 1939 film were not so much artistic as legal, since this was not released by the same studio. That's why there are still some homages, if it seemed like it could get past the legal department.