Every year, 90% of the teams get an A or B. The teams that don't are those who "reached" for someone according to the amateur beliefs of wannabe draft experts, or those who didn't fill a "team need" according to the amateur beliefs of wannabe GMs.
The odds are that most of these guys will bust, so luck is a huge factor, positional needs are almost never the same from one year to the next, and NFL teams pour in millions of dollars for scouting and investigators, while guys like Kiper and McShay go to Staples to buy an eraser board on their 70k salaries.
The mock drafts and "grades" are good entertainment; the post-draft "scores" that take place before these guys have even put on pads....insulting to one's intelligence.
In my opinion, the teams who you can say "won" the draft just based on what we know at the moment are those who created the most value by using real science rather than the Jimmie Johnson chart (in other words, typically a trade down of an overvalued high pick for a ransom) and those teams who drafted one or more QBs, since the draft still hasn't caught up with the positional value yet. Hitting a quarterback is like hitting on 6-7 other positions, whole missing on a quarterback is just one miss. I would advocate drafting 2-3 QBs, per draft for teams without a franchise QB. Until you get one, none of your other draft picks really matter much.