Am I the only one who didn't see any evidence of this?
And it happeened in The Pitt, Operation:Anchorage, and Mothership Zeta. I actually think it's a good thing because it makes it more challenging and you can more easily take new content back with you and try it out without being overencumbered.
The Pitt and Mothership Zeta you were able to retrieve all your items before the conclusion of the DLC. You weren't forced to use the new weapons and armor throughout the DLC.
Personally, I don't much care if we are stripped of our belongings upon entering the area. I rather enjoy the idea of a struggle to survive in an unknown area, instead of waltzing in all godlike and mowing everything down that gets in your way. Where's the fun in that, I can do that in New Vegas already.