There is a chorus of disapproval on the web today as Asus announced a full-fat Windows tablet  (Eee Slate EP121)  at CES in Las Vegas, along with three other devices running Google Android – the Eee Pad MeMo, the Eee Pad Transformer, and the Eee Pad Slider.

The most detailed “review” I’ve seen for the EP121 is on the Windows Experience Blog. Core i5, 4GB RAM, 64GB SSD, capacitive screen with touch and stylus input.

Nice in its way; but no kind of game-changer since this is an echo of early Windows slates which never achieved more than niche success. Four big disadvantages:

• Short battery life
• High price
• The stylus
• and another thing: in the rush to embrace touch computing, vendors appear to have forgotten one of the best features of those early tablets: you could rest your hand on the screen while writing with the pen. If you have a combined touch/stylus device that will not work.

Microsoft fans will be hoping CEO Steve Ballmer does not make too much of the EP121 and devices like this in tonight’s keynote. If he does, it will seem the company has learned little from failures of the past.

Asus deserves respect for introducing the netbook to the world in 2007, with the original Eee PC. It ran Linux, had an SSD in place of a hard drive, battery life was good, and above all it was light and cheap. Back then the story was how Microsoft missed the mark with its 2006 Origami project – small portable PCs running Windows – only to be shown how to do it by OEMs with simple netbooks at the right price.

Asus itself is not betting on Windows for tablet success; after all, three of the four products unveiled yesterday run Android. Despite what was apparently a poor CES press conference these may work out OK, though the prices look on the high side.

There will be many more tablets announced at CES, most of them running Android. Android “Honeycomb”, which is also Android 3.0 if Asus CEO Johnny Shih had his terminology right, is the first version created with tablet support in mind.

But why the tablet rush? The answer is obvious: it is because Apple has re-invented the category with the iPad. Since the iPad has succeeded where the Tablet PC failed, as a mass-market device, intuitively you would expect vendors to study what is right about it and to copy that, rather than repeating past mistakes. I think that includes long battery life and a touch-centric user interface; keyboard or stylus is OK as an optional extra but no more than that.

Equalling Apple’s design excellence and closed-but-seamless ecosystem is not possible for most manufacturers, but thanks to Android they can come up with devices that are better in other aspects: cheaper, more powerful, or with added features such as USB ports and Adobe Flash support.

It is reasonable to expect that at least a few of the CES tablets will succeed as not-quite iPads that hit the mark, just as Smartphones like the HTC Desire and Motorola Droid series have done with respect to the iPhone.

Microsoft? Ballmer’s main advantage is that expectations are low. Even if he exceeds those expectations, the abundance of Android tablets at CES shows how badly the company misjudged and mishandled the mobile market.

The implication for developers is that if you want app ubiquity, you have to develop for Android and iOS.

Microsoft could help itself and its developers by delivering a cross-platform runtime for the .NET Framework that would run on Android. I doubt Silverlight for Android would be technically difficult for Microsoft; but sadly after PDC it looks unlikely.