"The difference comes out in the specific type of LCD panel and in particular its backlighting. The U2713H (the one being discounted today) is aimed straight at graphics professionals who need highly accurate color representation on their display. Typical consumer-grade monitors can’t accurately represent the full spectrum of colors available, which becomes a critical issue for those who need to be able to create graphics or any other visual product with color, especially if it’s going to end up in print.
While the U2713HM uses a fairly common White-LED backlight, which offers slimmer packaging and less power consumption over traditional CCFL backlights, the downside comes with the limits to the color that the W-LED is able to produce.
The U2713H uses a new type of backlight comprised of green and blue LEDs (GB-LED), allowing it to cover 103% of the NTSC color gamuit, 99% of Adobe RGB, and more than 100% of the sRGB space. This new backlight combined with 10-bit color support (achieved with an 8-bit + FRC panel) gives the U2713H a color palette of 1.07 billion, compared to 16.7 million of the W-LED equipped U2713HM.
While users will unlikely be able to fully utilize the 10-bit color spectrum of the U2713H, it still allows for the critical wide color palette needed for such work. Of course, such capabilities are not new; there are many professional-class monitors on the market with comparable specs and features."
It looks like the monitors are fairly similar but 2713h is just better color potential. I might not ever use it, but why not own a more expensive monitor than a less one, if I don't have to pay anything.