I believe this is due to a number of factors including changing work habits, increased flexibility in scheduling, increased availability in prepackaged foods and ready made meals, and the fact that fewer people consider eating as a family around a dinner table to be important.
I first started noticing this trend in collage when, due to varied class times, I found myself eating at odd hours between classes. Even now, I have breakfast around 10, lunch at 3, and dinner sometime between 5 and 9.
Not saying that this is wrong or anything, just that it is changing.
Perhaps we should start calling them 1st, 2nd, 3rd, and 4th meal instead.