Not to mention all the NCR and robots actually on the strip...
So I guess that's the answer. It would be away to guarded to just kill a few guards then walk into 38 and kill Mr.House. At least it should be.
As for getting into the strip without taking the main quest. I am betting there are alot of ways to get in without doing the main quest. We don't even know what the main quest is yet. Getting the package back and dealing with
would be more of a personal quest.