The myth goes back to before SQL Server 6.5, which [added row level locking][1]. And hinted at here by [Kalen Delaney][2].

It was to do with "hot spots" of data page usage and the fact that a whole 2k page (SQL Server 7 moved to 8k pages) was locked, rather then an inserted row

Edit, Feb 2012

Found authoritative article by Kimberly L. Tripp

["The Clustered Index Debate Continues..."](http://www.sqlskills.com/blogs/kimberly/post/The-Clustered-Index-Debate-Continues.aspx )

> Hotspots were something that we greatly tried to avoid PRIOR to SQL Server 7.0 because of page level locking (and this is where the term hot spot became a negative term). In fact, it doesn't have to be a negative term. However, since the storage engine was rearchitected/redesigned (in SQL Server 7.0) and now includes true row level locking, this motivation (to avoid hotspots) is no longer there.

  [1]: http://www.windowsitpro.com/article/windows-client/sql-server-6-5-introduces-insert-row-locking.aspx
  [2]: http://sqlblog.com/blogs/kalen_delaney/archive/2009/05/03/controlling-lock-granularity.aspx