Well, I answered based on my personal needs. Theoretically I believe that it should be stated ethically, especially with a seller that normally provides multiple formats.
But as others stated as is we are lucky that they provide multiple formats that are more "open" (open in the sense that Adobe DRM works on different devices and programs that aren't kobo dependent). But as was also stated, the fact that they mention that they believe in open standards and proudly support epubs means they should try to apply it whenever possible (they at no point guarantee it, they only say they support it which is implicit but not explicit).
Now personally I said it was good to know but not necessary. I have bought 69 books from them, two from kindle (one because it wasn't available on any other site/seller and the other because while I was buying that one I saw one with an over 90% discount that seemed potentially interesting), and the two humble bundle ebook packages that have come out. The humble bundle offerings were DRM-free epubs so I just imported them onto the Glo and my phone's kobo app. The kindle ones... well, let's just say I have calibre but not a kindle and don't like their app.
Since I normally have a kobo device (Glo died and waiting on the Aura to become available online again) the only times I care about the format is when I want to read something that is only available on PDF. I have only bought one book that turned out to be a PDF which was SO utterly unreadable on the Glo and that was a complete mistake because I hadn't even considered the possibility (that was hell as converting PDFs to epubs often doesn't work out so well, especially if they have copious amounts of footnotes). And on two occasions I would have liked the book to have been available as a PDF (PDFs are easier to make handwritten notes in on devices like the Galaxy Note 10.1 which is great for studying/textbooks).
But yeah, I think that
most people are fine with either kepubs or epubs and don't care since if they're buying on kobo they most likely have a kobo device or use their app.
Don't forget that comics aren't even available for independent downloads, they can only be viewed on their app on tablets/phones, which to be frank makes me wonder if the limited availability of certain formats is sometimes somehow related to publisher restrictions placed on Kobo.
And hey, for me the format options appear on the book info page before purchasing so if I remember to check I can see the info
