Mu guess would be that the workload is a a lot higher on server A, plus you've got much more AWE memory for SQL Server to use - even so, it looks like the workloads are churning the memory somewhat. If two queries from separate customers are using lots of memory for disparate data, I'd expect to see what you're seeing.
Hope this helps
Paul Randal
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Blog:www.SQLskills.com/blogs/paul Twitter: @PaulRandal
SQL MVP, Microsoft RD, Contributing Editor of TechNet Magazine
Author of DBCC CHECKDB/repair (and other Storage Engine) code of SQL Server 2005