Schaub (already discussed), Pennington 20 attempts his first two years in the league, Vick already discussed), McNabb (216 rookie attempts, 49.1% completion, 69/133 as a starter--that's 51.8%--his career completion %), Eli Manning (finished rookie year completing 69.6, 51.4, and 66.7% of his passes), Jason Campbell (0 pass attempts as a rookie, 53.1% completion percentage second season is 7.7 points above his career), Kyle Orton (51.6% as a rookie, 58.1% for his career), Alex Smith(50.9% completions as a rookie, 57.1% for his career), Matt Hasselbeck (seriously, are you joking here? First season as a starter--he attempted 29 passes his first two years in the NFL--54.8% completion, 60.1% for his career), Trent Green (attempted 1 pass in his first four NFL seasons, first season with more than 1 attempt, he complted 54.6% of his passes, and his career completion % is 60.6), Steve McNair (attempted 80 passes as a rookie (4 games 2 starts); second season attempted 143 and completed 61.3% of those passes--actually better than his career rate).
I'm done looking people up. All those guys went from high 40-low 50% passers in their first year or two, to high 50-low 60% passers by their 4th year.
The players who started out in the high 50s to low 60s saw negligible progress in their completion % whereas almost every player who started poorly in that department and continued to start, jumped at least to the high 50s.
K9, I think there is a sort of regression towards the mean with completion % with QBs, where the poor ones as they refine the flaws in their games can consistently get to the high 50s to low 60s. Adequate at least, and the worse they were to begin with the bigger leap they appeared to make. Rarely do they reach the mid 60s that only a few QBs ever do. Point is that it is not the exception but the rule that QBs who continue to start become at least 58% passers after two years. The exception are guys like DA who for whatever reason can't adjust their game.
If you don't like Skelton, base it on something rational. Don't base it on something historically inaccurate like a so called inability to improve their completion percentage by 10%.