Because there was a screenshot somewhere showing part of the "character sheet" part of the interface and there were no attributes visible and nobody from Bethesda has categorically refuted the "OMG no attributes?!?" claim.
Short version: Blatant assumption based on dodgy information or lack thereof.
Yes I assume so myself, lack clear confirmation that they are out and lack of RPG games without it.
Yes as other says, it’s quite possible to make an rpg without them, but why bother, you either give everybody the same properties like speed, carrying and jumping capabilities, you calculate them with some special method under the hood or you use attributes.
Yes you can use perks, we had perks that made you stronger in Fallout 3, and they raised the strength attribute.
More probably explanation, attributes are inn but far more in the background than I Oblivion. They are raised automatically on skill increase and / or by perks like in fallout.
Probably less important than in Oblivion, skills are also less important because of the perks.
They have not shown the attribute page as it looks like the skill one except more boring.