why is it that whenever i play one of chessmaster's lesser alter ego's (one of the 1400-1700 personas), and as usual i play my Barcza, why do they almost always sac their knight for a kingside pawn?  sure the results are 50/50 when they do... (i don't always beat them when they sac)   but is that a good strategy, maybe just good against my barcza?  or should I be winning more easily in these games?

In general, unpredictable and tactical personae at the 1500 level do this to give themselves a handicap and/or steer the game into tactical lines. It's not hard to find personae in that range who rarely or never do such things... you can view the characteristics of each persona before playing them. When I play computer opponets, I prefer to play a mix of tactical and positional personae since each tests slightly different skills.