NEW YORK ( TheStreet) -- Microsoft ( MSFT) unveiled improved versions of its two tablet-laptop combo devices: One based on Intel ( INTC); the other based on ARM, in this case Nvidia's ( NVDA) Tegra 4. My prediction is that sales success will largely elude Microsoft yet again.First of all, however, let me point out that both new Surface versions are solid improvements over their predecessors. The screens are better, the processors are faster and more power-efficient and there are exciting new peripherals -- keyboards and docks. Microsoft's argument for the Surface remains what it was the first time around, a year ago: Laptop and tablet, all in one! I will explain why this just doesn't work out. If your objective is to use a laptop for anything more than an hour's worth of tortured play, you need to have a screen that's larger than 12 inches, preferably at least 13 inches. In addition, you need the keyboard to be large enough. The Microsoft Surface fails this essential test. It has a 10.6-inch screen, and a resulting cramped keyboard. This is OK for a small child. It is unsuitable for working adults. The other problem is the relationship between the keyboard and the screen. In a regular laptop, the bulk of the weight resides under the keyboard, and the screen is held up by a hinge that inherently must be "stiff" so that the screen stays in place at the desired angle, no matter how you move the laptop around. In contrast, the Surface has almost all its weight in the "screen" portion. Then, the keyboard is attached to the screen with a "limp" magnet/hinge combo. That's great in one way because it makes it detachable, but it also makes it very difficult to use the device unless it's placed on a hard and flat surface (no pun . . . ). The problem is, that often enough, I place my laptop on places other than a hard/flat surface. It's sometimes in my lap, sometimes in my hands when I'm laying on the sofa or in bed, or sometimes on a very shallow table where part of the laptop's base sticks out.