A user posted a screenshot of its Windows 10 Build 10074 on winbeta and I just realized that the start menu is not blurred, so is this because that I have installed the leaked 10074 by WZOR and not the one by Microsoft ?
It's a A/B field test by MS, not everyone gets Blur enabled from the start. Can be changed via a simple Regedit switch. Search the forums for "EnableBlurBehind". People in group B only got blue paint.