Kobo is telling me that ADE doesn't support EPUB3 and I can't download certain books -- how do I fix this?

The last book I purchased on Kobo.com is apparently in epub3 format and won't download -- kobo's customer service tells me it's because ADE doesn't support the format. This would seem to be a problem that will only get worse. One: is this true? Two: shouldn't it? Three: is it fixable?