I'll give you this as an example, I swing 100 times to land 100 hits in 100 seconds...you swing 100 times to land 99 times ... Isn't my dps still higher?
In general, giving up a small amount of hit or exp to gain secondary stats won't be a terrible loss.
Using your example above:
If each of your 100 hits lands for 100 damage (avg), you made 10,000 damage in 100 seconds, for 100 dps.
If each of my 99 hits lands for 102 damage (avg) (because I traded Hit into Mastery, for example), I made 10,98 for 101 dps.
Also, in this particular case, we're talking about haste.
If you make 100 attacks and score 100 hits in 100 seconds at 100 damage each, you've made 100 dps.
If I make 102 attacks (because I have more haste) and score 101 hits (and 1 miss because I have less hit) in 100 seconds,
at 100 damage each, I've made 101 dps.
Obviously these numbers are completely made up, but the point is, missing occasionally (and we're talking very occasionally
) isn't necessarily a dps loss, if you traded those misses for attacks that hit harder or happen faster. Which is where the complicated math comes in, and that's why we run simulations.
It's pretty complex to determine exactly how valuable those last few percent of Hit and Expertise are in relation to the other secondary stats. Clearly no one is going to tell you to run around with 3% Hit Rating in PvE. Even if the gains in secondary stats averaged out (over tens of thousands of attacks) to a higher dps (which I doubt would happen), there would still be the functional problem of large stretches of time where you were missing many attacks in a row. Nobody wants that.
Hitting almost all the time is good. Having a compulsion to never miss
isn't necessarily optimal, though.