According to the rumour, it depends on how the tablet is used. In a game where the tablet is used intensively (as in a different view of the game with all the in game effects used) then the TV view will "just" look better than the port. On the other hand if it's used just as a map/hub, then much more can be done.

Here's what the guy who is the originator of the rumour also had to say:

My yesterday post IS NOT a metric evaluation of the Wii U capacities, it can't be treated as that, i thought i made myself perfectly clear with how much i stressed on the specific context. It's just an information about how some third-parties, with particular titles (ports), with a certain approach of the padlet (intricate), with a dev kit (v4), in a certain step of development (far from being polished visually so it'll look even better in the end) + other parameters, handle the Wii U hardware. And still, it's rather impressive, some techies explained how rendering a complex scene on a 480p screen is taxing, and this is IN ADDITION to a graphically ambitious content displayed in a solid 720p on the main screen, nicer than its current gen hd counterpart. Nothing to be disappointed of, really, except if some gafers were in the "1080p for every titles at launch" camp.

Interesting. I have no doubt that Ninty first party will bring the most out of the system anyways. Do you think we will get a finalized spec list at or around E3? Since the launch is nearing I can't imagine there being more dev kit revisions

I saw this earlier and my impression is that it goes against what Nintendo said at E3. They stated it should have 1080p with 30 or 60fps.

Now if that means 720p to get stable 60fps or 1080p for 30fps average.... well I can see that and it is still a solid upgrade from PS360 where its all 720p at 30fps or less.

Also, it states 720p when using the controller screen... so with out that its probably solid 1080p.

The controller is also potentially off as they've always said it will be HD and 480p is not HD. But in reality, it would be fine for a 6" screen.

Considering recent rumors state they actually upgraded the system some so it will be compatible with Unreal Engine 4... idk if this rumor is perfect. But, it is believable.

It says "720p for games running intensive visuals on the controller". That means that, if you're going to be looking for live-action in-game displaying on the controller (meaning visuals like the TV screen, but on the controller), then it'll need to cut down to 720p for good framerates. But I highly doubt most titles will use those kinds of visuals. Zelda, for instance, the way it was demo'd at E3? That's not "intensive" visuals. Zelda could easily pull off 1080p.

And multiplat titles likely won't utilize very much controller screen action, so every single one of those will easily be able to pull off 1080p, no questions asked.

It's only titles with features unique to the WiiU that will have to scale down, and even in those, it's only going to be a certain few that are pushing a lot of action on both screens.

But I'm not worried about it. Games are going to be awesome and beautiful regardless.