SQL Server Express Limitation
No, it does't, and never did. 

The post you link links to the blog http://blogs.msdn.com/b/sqlexpress/archive/2008/02/22/sql-express-behaviors-idle-time-resources-usage-auto-close-and-user-instances.aspx that explains that the 'instance going to sleep' is a RANU behavior (user instance), not an Express behavior. As you plan to move from Standard to Express, is obvious that that you do not plan to move to user instances (RANU).