It's not unusual for me to see applicants with 700+ Verbal GRE and 3 AWA or less. You can cram for verbal part, learn all the key vocabularies, tricks and get a very high scores. Applicants from Korea, China are experts in this area.
You can't just do the same thing in the AWA section. I got 4.5 the first time I took GRE back in 2004 and all I did was to look at few sample essays. The key, in my opinion is to get yourself comfortable with writing long augmentative essays to defend your opinion.
And online forums like Quantnet provide an excellent playground to sharpen your pen. (You can't use one liners like "LOL...OMG, that shiz iz the shizzle" to improve your writing). Reading Op-ed sections on NYT or such would give you idea how people can have 100% valid and opposite essay on the same question. You can do that if GRE is the first time you try to do that in English.
If I remember correctly, 3 people grade the essay and 2 people have to agree on the same AWA score. So, it's not one person deciding how much your writing is worth.