Asus K40Ab or K50Ab... as usual...

K40Ab is 14", K50Ab is 15", and with a numpad...

other than that, nope...

Let me assume you were asking about the difference in users' experience between the two models above.

Both 14in and 15in screen above are using the similar resolution of 1366 x 768 pixels, hence, this fact alone may translate to the following users' experiences :

1) Compare to the 14in, the 15in K50 has a thicker taskbar, bigger icons, larger fonts.

2) Due to 1) above, some ppl feel that the 14in's color display looks 'sharper' n more 'elegant' to the eyes.

3) Due to 1) above, when playing High Definition Video, some ppl feel that the 14in display gives a better 'HD' feeling than the 15in. Note that it's about the quality of video "perceived" not the size of the video.

4) With the 14in K40 running on batteries, users may have a better luck to enjoy the complete 2hours 28min of "Transformers-Revenge of the Fallen" on the plane or train or spaceship to Mars. 

5) Some ppl may think that "Size really matters" especially some girls out there in the middle of the night, who may think the extra ONE inch in K50 is more desirable/enjoyable. Of course, the 14in is longer lasting but shorter by an INCH. 

I hope this little piece of information above is of a little bit more helps for those who's considering both the K series model above.