http://patentlyo.com/patent/2007/04/patent_jurisdic.html does a good job of explaining.

Basically, the federal circuit's view of 28 USC 1391 is very different than 28 USC 1400.

If you look at cases prior to VE Holdings, they view 28 USC 1400, and in particular, the definition of "resides", very narrowly (to principal place of business/corp hq).

If you look at VE Holdings, and their view on 28 USC 1391, you can see it greatly expands the definition of "resides" to include essentially everywhere.

The old language of the law had a requirement for "regular and established place of business" before suit could be filed. The new language requires "personal jurisdiction at the time the action is commenced".

The key difference is in whether or not you must have an established place of business for a suit to be brought against you in a jurisdiction.