wilderness - 9:18 pm on Dec 6, 2012 (gmt 0)
From what I can tell according to the documentation at apache.org, the regex for the user agent string can be enclosed in quotes, so I don't think it's doing an exact match,
Try the following two lines (not simultaneously) and you'll see that enclosing within quotes does exactly that
SetEnvIf User-Agent "chrome"
SetEnvIf User-Agent "Chrome"
The first will always fail because no Chrome browser uses the lower-case c.
The second will deny every Chrome visitor to your site (s).
I use quote very sparingly due to this conflict.