Guess how many Red Sox 1st round draft picks have made the majors between 2008-2012.
I'm not sure why you limited this to the 1st round. For example, Lavarnway was drafted in the 6th round in 2008 and made the majors last year. Your overall point is a good one. Players drafted in 2008 or later are not terribly likely to have made the majors already for any franchise, but the choice to limit your response to round 1 seems odd.
To expand on your list a bit here are the players drafted between 2008 and 2012 who have seen major league action (with or without the team that drafted them).
Red Sox: Ryan Lavarnway, Kyle Weiland, Stephen Fife, Tim Federowicz
Yankees: D.J. Mitchell, David Phelps, Adam Warren,
Blue Jays: David Cooper, Tyler Pastornicky, Eric Thames, Evan Crawford, Danny Farguhar, Chad Jenkins, Aaron Loup, Drew Hutchinson, Sam Dyson
Orioles: Bryan Matusz, Xavier Avery, Kyle Hudson, Manny Machado
So in that time you're looking at two, maybe three players who look to be major league regulars and a bunch of minor league depth that have seen a handful of innings or games each developed between the five teams of the AL East from 2008-2012. So the point that judging the Rays by their lack of major league players drafted in that time frame still stands, but they are the only team in that mix that hasn't seen contributions from anyone drafted in that period. Part of that is the health of their pitching staffs has been excellent, which minimizes the need for calling up guys like Fife or Weiland, though. So I don't know if it's really a bad thing that Tampa hasn't had anyone crack the majors from those drafts. Plus, it's not like they have a weak farm system right now.