I think Bruce is his own man who doesn't feel the need to answer to his parents (or their grave) for every failure. Obviously it's important to recognize the importance of the Wayne's, but it's also necessary to accept that Bruce is a grown man who is past their deaths (or as past them as is possible for Batman), and continues his crusade because it's what's right, not because it satisfies his sense of loss or desire for vengeance.
That may have been how his campaign started, it may have been the case when he was an angry young man, but I think we've gotten far enough along (in the comics, and perhaps in the films as well) that we don't need to be talking about the Wayne's all the time now. I wouldn't be adverse to "grave visiting" in the proper context, necessarily, I just think it's important that we recognize that Bruce isn't thinking "Damn, I failed my parents!" He has far truer motivations than that. When weighed against justice and the welfare of Gotham, failing his parents should be the last thing he's concerned with.