If you think about it, jumping ahead to Xbox 8 even though its only the third Xbox seems weird, but is that really any different from jumping from the Xbox 1 to the Xbox 360? Its the same basic principle. Sony will almost certainly name their next console PS4 so by having an Xbox 8 it kinda gives an impression that its 4 models ahead of the PS4.... that's not true of course, and anyone with even the most basic knowledge of this stuff would know better, but its something that could dupe the casual uninformed crowd.
People who don't know any better will look at the Xbox 8 and think "Wow! This Xbox brand must be really good if its been around so long that its now up to its 8th generation. It must be tried and true, unlike that Playstation brand which has only been around half that long."