Yes, ASHRAE 90.1-2007 requires vestibules. Therefore it becomes a requirement in LEED v3. In many states, vestibules were already required as part of the building code already.
There are exceptions in 90.1, as follows (summary):
1) if you have revolving doors
2) if it is an "emergency egress" only door
3) buildings in a mild climate
4) small buildings in moderate climate
5) very small buildings in any climate
In cold climates, vestibules are a very good way to prevent heat loss and infiltration. If you don't meet the exceptions above, instead of working to "get around" this requirement, I think you should figure out how to accommodate them.