I think that the comparison is not flattering and biased. The lenses are so different for example ... the k-x has a small lens and the K-7 is bigger lens.
I tried both the K-x and K-7 with the 18-55WR and later with the 18-250mm. At the time I also tried the D90. Here are my thoughts.
The K-x and K-7 with the 18-55WR are very close compared to the D90 with the canon IS kit lens. The differences in size between K-x and K-7 are relatively small and personal feels might differ. The K-x is slightly smaller than the K-7 but the buttons are more cramped than those of the K-7. The touch of the K-x feels more plastic than the K-7 and D90. The K-7 was the more sturdy body. The grip of both K-x and K-7 is very good.
With the 18-250mm, I feel that the K-7 is better balanced than the K-x. The size and weight of the K-x with the 18-250mm is nearly identical to that of the K-7 with the 18-250mm. Since I use the 18-250mm as my primary lens, I see no size difference between Kx+18-2500 + K7+18-250. Both fit in the same type of top loader bag.
In conclusion: if you use a pan cake lens, the K-x will have a size advantage if "smaller is better". If you use a heavier lens (eg 18-250mm), there is little size difference and the weight balance is nicer with the K-7.
Hope that the comment will help...