A363: You don't need levels in crusader to take Thicket of Blades. You could be an insane fighter who took Martial Study (a devoted spirit maneuver), Martial Stance (Iron Guard's Glare, since you need a 1st level stance before you can take a 3rd level one), and then Martial Stance (Thicket of Blades) at 10th level (IL 5 in all martial adept classes for a non-"martial" class like a fighter).
In your example, the Warblade 4/Crusader 2 couldn't take it, because he'd have an IL of 4 as a crusader (and an IL of 5 as a warblade) when he got his 2nd stance as a crusader. But a warblade 6/crusader 2 (IL 5 crusader, IL 7 warblade) could take Thicket of Blades, and actually would get it at the same level as a straight crusader would.