TDR actually has a worthwhile gate next door though to help keep numbers in check. The only times I've been to TDR it's been slow to pretty dead (of course one was May 2011 after the earthquake). I realize those times are few and far between though.
You will be in for a real treat when you go on one of the increasingly common 90,000 to 100,000 guests days, then!

Actually, Tokyo Disneyland does a great job of soaking up crowds, and as you can expect, crowd control is exceptional. We were there on a couple of days last Christmas-season during which tickets were sold out days in advance. Of course, our perception of crowd management might have helped by Country Bear Christmas, which was our main interest, and even on a capacity day, shows are only 75% full.
Those 85,000+ guest days (aka "weekends") and the fact that we
know TEA's numbers for Tokyo Disneyland are accurate are my basis for questioning whether the WDW numbers are inflated. Even if the two parks are hitting ~40,000/guests on an average weekday, Magic Kingdom isn't nearly as crowded as Tokyo Disneyland is virtually every weekend of the year.
I just don't see how you get to 18m for MK and 17m for TDL unless you're liberally counting park hoppers. In that case, it makes sense, as park hopping is uncommon at TDR.