[VBCurtis]

Two problems: First, determining return on a specific hand in a specific position is really quite thorny. There is room here for some difference of opinion, in addition to adjustments to starting hand tables based on the players in the blinds. If you wish to ignore who the specific opponents are, then you're talking $1/2 poker, which isn't addressing anything in mid-high.

Second, if we ignore differences of opinion, your questions boils down to "why do people play bad?", since you're asking why they're inconsistent in their choices of hands that are (in theory) the same EV. Shania is one answer-- play members of a small class of -EV hands on occasion so that your play is less predictable. Perhaps I see your original curiosity about identical +EV hands being played sometimes and not others; this is simply people play bad, esp at low stakes. You won't find people in Mid-Hi that make these sorts of mistakes, so they don't understand why you're asking about a player who would. At $1/2, they make these mistakes, and we make money off those mistakes. At $15/30, we make money almost solely off post-flop mistakes, as the preflop mistakes are tiny/rare. Looking at pre-flop only is reinventing the wheel, and perhaps 5% of poker understanding (though often enough to beat the easiest games).
-Curtis