Sort Order Of Aspnet_Users Table?

I am wondering if the aspnet_Users table is always sorted (by UserName) even if I add new users which are alphabetically between two already existing users.

I've noticed that the method Membership.GetAllUsers() always seems to return a sorted collection of MembershipUsers.

Also when I look into SQL Server Management Studio and run a simple SQL query without ORDERBY clause...

SELECT [UserName]
FROM [MyDb].[dbo].[aspnet_Users]

...I get always a sorted result list.

I'm still very unfamiliar with SQL Server but I expected that when I add a new row to a table it is (physically) appended to the end of the table. And when I run a select statement without ORDERBY the rows will be selected in the order they were initially inserted into the database (so without any specific sort order).

I am wrong I guess. But how does it really work? Is it perhaps something special with the aspnet_Users table?

I am happy that the MemberShipUserCollection returned by GetAllUsers() is sorted but is it always guaranteed?

Update

I've just noticed that the database contains a stored procedure called aspnet_Membership_GetAllUsers. This procedure actually contains an ORDER BY clause by UserName. So if this stored procedure is indeed always called when I use Membership.GetAllUsers() in my code (at least if I am using the SqlMembershipProvider) it explains why the collection returned by Membership.GetAllUsers() is sorted by UserName.

Remains the question: Is Membership.GetAllUsers() actually based on this stored procedure?