If I can be slightly unpleasant, whatever your religious bent or not, our bodies are just clever machines and it is the effect we have on people and the memories that we leave them with that matter. Not where our physical bits end up after death.
Everyone deals differently, some cry, some go quiet, some laugh. Are any of these people wrong? Not at all, losing someone is dreadful and no one should feel guilty for not being able to tend a grave afterwards be that for geographical reasons or emotional.
Do I think tending a grave is bad? No, not one iota. I just personally didn't want to.