You'd be surprised at how petty some (otherwise very intelligent) people can be.
At a former job, the company paid to send some of team A to a conference for platform B ($1100 / head), while some from team C were sent to conference D ($500 / head). When one member from team C found out about the price difference between the two conferences, he started bellyaching and said the company owed him another $600.
*Not saying that being offended is always bad--there are things that one reasonably might be offended by, just that this is one of them.
(Because "there are some X which are Y, but this X is not one of them" is a pattern I recognize as common, and "there are some X which are Y, but this is one of them" is not a pattern that I am familiar with)
I always hear this argument, and I wonder how often it really applies. I have coworkers who do basically the same job as me but get paid twice or more what I do for it. I don't sit around being jealous, I think about how I know it's possible for me to get paid that much and that's something I can aspire to. I suppose in other words, it's information about the salary ceiling. (Of course, that's still an incentive for management to try to make sure I don't know other people's salaries.)
I've never heard anyone, in this environment or at my last job, complain enviously about other people making more money than them. The most I've ever heard on the subject is me and a couple other guys shook our heads discussing another guy who made much less money than we did and definitely deserved more.