My general experience with plowing with 1/2-tons is that, yes... they do break a little sooner than the 3/4-1-ton trucks, BUT, the parts that do break are generally a lot cheaper than the others. Any truck you abuse will eventually break. If you plow with a "sane" mind (and I use that term loosly) your truck will last a long time, even while plowing. Also general maintainance plays a HUGE part in it.
Also, with small improvements, such as heavier springs, load supports, and frame reinforcing, you help rule out items that tend to break. I've owned my current Z71 for about a year now, have put about 13,000 miles on it, and I've changed the oil every time it starts getting dirty, and Ive changed the trans-fluid about four times. I also change the front and rear differential fluids once a year, and the transfer case before every winter. Little things can save you big $$$...
Just my $0.02
-Tim