actually, while each of those interpretations are valid points, i mean something entirely different:
you are rendering each piece of grass as though it is an object.
it is not.
it is a detail on the tile.
the tile is a detail in the grass.
the grass is a region of the ground.
the ground is one object.
ONE CHARACTER OR LANDMARK is as important as the ENTIRE GROUND. If the ground is like a character, then the grass is like his shirt, a tile like his sleeve, and the tile a single button. You have to render it as such or your background will never work well. zyndikate does have this pretty much down pat in his grass because he is rendering for a field, not individual blades of grass, although there is a slight issue in his where the dirt tiles and the grass tiles are fighting each other in a way that they shouldn't. Senad's tile is also great for the same reasons.
if you aren't sure how to go about reducing importance, here's a tip:
contours: really, the ground shoudn't create it's own strong contours. it's the ground! it's bounds by itself are infinite, and will be defined for practical purposes only by the objects that breaks its continuity. Contours and outlines should be saved just for objects. By otlining every piece of grass, you are telling the player that every blade of grass is as important as his character.
local contrast: local contrast defines importance. The faster something changes from light to dark, gray to color, or hue across the color wheel, the more important it is. That's why, for the most part, outlines and strong contrast should define characters and not be used in a single tile. The entire background might (might!) have as much total contrast as a character (and usually doesn't!), but an individual ground tile should still be fairly slow.
