Almost two years ago, I blogged that Lock Pages in Memory was finally available to Standard Edition customers (Enterprise Edition customers had long been deemed smart enough to not abuse this feature). In addition to applying a cumulative update (2005 SP3 CU4 or 2008 SP1 CU2), in order to take advantage of LPIM, you also had to enable trace flag 845.
Since the trace flag isn't documented for SQL Server 2008 R2, several of us in the community assumed that it was no longer required (since it was introduced before 2008 R2 went RTM, and a trace flag is typically only introduced to change behavior after a product has been released). We don't expect to see documentation stating that something *isn't* required, just like we don't expect to find a page on the SQL Server site that lists all of the features not supported by SQL Server.
As it turns out, the trace flag is still required for SQL Server 2008 R2. Hopefully they will update R2's Books Online to reflect this (and Denali's, if it continues to be true for the next version of SQL Server).