I am using both a 5n and a a65. The reason is fairly simple I had an investment in old A mount Minolta lens and they work well on the 2 bodies. The 5n is almost the perfect size for a camera that I actually will carry and use. The pictures are quite good and peak focusing is a big help. I use the electronic viewfinder on it and it really helps as well.
The 65a fills in the gap for me for a heavier medium size body. I like to shoot wildlife and the bigger heavier body is easier to keep stable on a tripod in wind, and pans a bit better. I like the menus/controls better on it as well. However I have the 5n setup quite nicely too. The big things you gain with DSLR bodies is better flash support, external mics (variety ) , battery grips etc. I just was tired of hauling big, bulky cameras for features I seldom need or use. I went smaller and shoot more as a result with a couple lens and a smaller monopod much of the time
Personally I look at 3 musts - easy control of ISO, Aperture and Shutter. The rest of the menu systems I don't use as much so it's not as important. My favorite layout is on Nikons but I have adapted to the Sony 's well