They are 3 different things that server 3 different needs. It's ridiculous to even imagine that you could combine them into one device given the consumer technology right now. Maybe in 20 years, when it's commonplace to sport a holographic projector on a phone, or screens can be unfolded and folded at a whim, then perhaps the tablet and phone can be combined into one (satisfying the needs that a personal computer satisfies would require significant advances in input technology).
A jack of all trades does nothing well at all. That seems to describe the Windows (Mobile and Desktop) strategy right now.
I agree with you. It's ridiculous to even imagine that you could combine them into one device given the consumer technology right now.
However, the phone can be connected to a dock so that:
b) Can be used as a tablet: see the Asus Pad Fone http://event.asus.com/mobile/padfone/
c) Can be used as a computer: Motorola Atrix has a dock with HDMI port and USB port.
d) Can be used as a game console. Let's compare the specs of an iphone s against a xbox 360:
* RAM Memory: xbox360 512MB RAM. iphone 4s 512MB RAM
* Triangles/sec: xbox 360 500 Million. iphone 4s 68 MPolygon/s.
* Filtered Texture Fetch: xbox 360 8.0 Billion Texels/sec. iphone 4s 1000 MTexels/s
iphone A5 cpu is manufactured using a 45nm process. intel is producing its Ivy Bridge processors using a 22nm process right now (see http://www.tomshardware.com/news/ivy-bridge-processor-release-22nm-3d-transistor,13753.html: "CEO Paul Otellini confirmed that Ivy Bridge 22 nm processor volume production has already begun, which is a rather significant achievement as there have been apparently no major hiccups in the implementation of its 3D transistor technology")
Of course, the next xbox will be more powerful than any smartphone, but think about having current xbox 360 games in your smartphone in 2013 or 2014.
* Xbox 360 http://www.pvcmuseum.com/games/vs/ps3-vs-xbox-360-gpu-specs.htm
* iphone 4s: http://en.wikipedia.org/wiki/Apple_A5