Ironically, both parties' primary strategies seem to have backfired.
DNC and RNC both would like to see mainstream, establishment nominees.
One of the big reasons Trump is now favored to win is that many Republican contests are winner-take-all. This primary strategy would have seemed to assure that a non-mainstream candidate (almost certainly unlikely to *win* many contests) could not easily amass enough delegates to be a serious factor at the convention. Surprise, that strategy backfires if your non-mainstream candidate actually starts coming in first!
One of the big reasons Hillary can't easily put Bernie away despite everyone expecting her to win most of the early contests is that these contests are NOT winner-take-all, meaning her "nuisance" competitor can actually manage to win significant delegates even in states he loses. This may help him hold on until the calendar is more favorable to him.
If Republicans awarded more delegates proportionally, things would be tougher for Trump... in particular, Cruz could be a much bigger threat, see: http://fivethirtyeight.com/features/ted-cruz-has-a-huge-math-problem/
If Democrats awarded some states (Texas, for example) in a winner-take-all manner, things would be a lot easier for Hillary.
Funny how each party tries to plan for the result they want, and each ended up with a plan that does the opposite. (Though at least for the Dems, math so far still does favor Hillary.)