It might be about ego in some cases (it shouldn't be). If there is some legitimate reason why I might have missed something that could affect my call, I don't have any problem with a coach asking me to check with my partner to see if he had something different.
A pulled foot or swipe tag at first base are two of the specific reasons listed in most umpire manuals where it's recommended that an umpire check with his partner- and you should check, if there is any doubt in your mind that you had a bad angle or your view was blocked on the play. Other examples on other plays might be if you know you were caught out of position or if there is an issue about loss of ball control on a tag or catch that you may not have seen.
I wouldn't go so far as to say that only a "good" umpire will ask for help. I would say that a "good" umpire will gladly ask for help when the circumstances warrant that he should. Not all calls warrant this.
Example: You're the base umpire and there is a very close force play at second base. You're in perfect position, you saw the tag of the base, the fielder maintained control of the ball and you judged that the ball beat the runner. There was nothing unusual here and it was, in your mind, a routine play that you called as you saw it- an out.
If a coach asked you to "go for help" on that one, would you? I hope not! Wanting you to ask for help on a routine play is nothing more than a coach who didn't like the call and is fishing for a second opinion. Are you going to allow that on every close play where a coach just didn't like the outcome? Be ready for a long day at the old ballpark!
Of all the dozens of calls an umpire might make in a game, there are really very few legitimate times when he should be asking for help from his partner(s). If the situation warrants, by all means do. But if it doesn't, I don't have any problem with an umpire telling a coach that it was his call, explaining what he had and sticking with it.
"Getting the call right" is one thing. If there's a reasonable possibility that your partner saw something you didn't, by all means, ask. Where I see this go down the wrong road is when umpires shirk their own responsibility to make calls that are clearly their's and dump the call off to their partner when they shouldn't, when umpires refuse to ask for help on calls that they should, or when coaches want an umpire to ask for help on routine plays that they don't have any legitimate reason asking about.