If you really want to know how complex standing up the Iraqi defense forces is, I recommend you go here to C-Span and watch LTG Petraeus's briefing to the Pentagon Press Corps on what he and his staff have been up to in the past couple of years. It's an interesting look at priorities, progress, logistics, and readiness assessments (which have been in the news so much today. C-Span may be reshowing it, too (I caught it this morning...).
Answers a lot of the annoying and nagging questions about why it takes so long for the "Iraqiazation" process.
UPDATE: GlobalSecurity summary here.