You need to consider the problems of getting data in and out of a tablet. A decent laptop will have a built-in optical (i.e. DVD) drive, so that you can load programs from it., or transfer data using CDs and DVDs (or simply play them). It also has a keyboard and either a trackball or a mouse, which provide far more efficient ways of getting data into the device than those offered by any tablet.
There's a good (but rather technical) article here:
http://www.techradar....hould-you-buy--691600
but this provides a briefer summary:
http://www.buzzle.com...k-before-you-buy.html
but for a REALLY scientific comparison . . .