This stuff makes for a great discussion. Not being a SABR-metrician (or fluent in English), I love this sort of stuff. It seems to me, that in order to come closer to a definitive trend, we would need:
Top 10 picks for the last 10 (maybe 15) years.
Sort them out by Pitchers v. Position guys.
Time from Draft date to time when they "stuck" in the big leagues (maybe defined as at least 1/2 a season of continuous service).
Min. number of game appearance in the show to be eligible to be called a Big League player (25? 50? 75? 100? more?)
Then you can look at what % of Pitchers "make it"; what % of Position guys "make it"; average development time before Pitchers make it; average development time before Position guys make it; and are there statistically significant differences between the numbers?
If you look further back in time, you could also measure length of productive career of Top 10 picks versus lower picks. Do the guys taken earl in the draft produce more over time than the guys taken lower? Pitchers? Position guys?
Gosh ... if somebody is willing to dig this up and crunch the numbers, I hope you will post them. It's beyond me for sure
Great stuff