Given that they require schema modification locks, why are sparse columns considered an alternative to EAV?

_Pro SQL Server Relational Database Design and Implementation: Best Practices for Scalability and Performance_ is a very reliable source of good database design ideas. As an alternative to Entity-Attribute-Value it suggests using dynamic SQL to allow your users to add new sparse columns to a table. To me, this idea stinks. Adding new columns requires a schema modification lock. This is a very serious lock and I would rather my users not have the ability to obtain it. Is there any property of sparse columns that makes allowing users to take such a serious lock not as terrible as it would be for other types of column?