Ergonomics are important for a couple reasons:
First, you're using the tool constantly for a few years. I'll give you an example, last year a friend had a DSLR from a different brand and asked me to take some photos at a party with it. The grip design was VERY uncomfortable for me. Just didn't like it at all. Even within same brand another friend has a smaller DSLR - I didn't like it - the controls were too close for my hand size. So you want to find out if you just really dislike a given camera before buying it blind from the internet.
Second, controls and menu layouts are somewhat consistent within brand - sure a 1dIV is different than a T1i but you'll find within a level of brand the layout and menus and such are similar. One may appeal to you over another. Or you may not care. If you hold a Canon 50d and a Canon 20d (3 generations apart) the feel and layout and operations are pretty close - the bigest difference being the larger LCD screen - but general ergonomics haven't changed much. Now, on the flip side is - every now and then a hiccup can occur - the 60d is NOT the same mag-alloy construction - it's plastic on the outside. So while controls are somewhat consistent and grip style is as well, the "feel" is different.
Again, you're looking at the two top camera systems available - largest selections of new lenses, largest upgrade path and largest likelihood of staying in the DSLR business.