James Anderson was simply overshadowed for most of his college career playing on a less than stellar team. He played at Oklahoma State, not Pitt or in the Big East amongst the East Coast hype machine, his college career ended with an early exit from the tournament and he saw his stock slip due to an injury that kept him from playing at 100%; the majority of mock drafts still had him going around 16 throughout most of the pre-draft.
Factor in that he wasn't able to prove his worth during the Vegas Summer League and get fans worked up over future prospects, and it's easy to see why there just isn't much hype -- never mind the fact that good-to-great college scorers that don't possess elite size or athleticism are generally question marks at a much greater level than rebounders, the one aspect that translates better than any other facet of the college game.
Bottom line, Anderson seemed and felt like a 20 pick. He could be great he could be "meh." We just don't know and we've yet to get a glimpse at the next level to gauge. DeJuan Blair never looked or felt like a 37. Everyone knew the guy was deserving to go in the Draft Lottery had there been no question marks due to health. The Spurs lucked out, were put a a no-lose situation picking him in the second round with no first round guaranteed money and the guy had left a mark on college basketball, the draft process and during summer league play that had the masses all riled up and jacked about his future prospects.
Anderson basically seemed an expected talent at 20 (maybe a little better) and Blair felt like a steal or godsend. Throw in the recent successes of Millsap and Landry and the lack of real success for scorers the likes of Anderson in college ball, and you've got your answer: different players; different cir stance; different hype.