Add Expires headers on Yslow doesn't have any effect - .htaccess

Question

I have mod_expires and mod_headers enabled on the server and this code in htaccess:
<FilesMatch "\.(htm|html|xhtml|css|js|php)$">
AddDefaultCharset UTF-8
Header set Content-Language "en-US"
</FilesMatch>
<IfModule mod_headers.c>
Header set Vary "Accept-Encoding"
</IfModule>
php_value session.cookie_domain "www.domain.com"
Options -Indexes
# year
<FilesMatch "\.(ico|pdf|flv|jpg|jpeg|png|gif|swf|mp3|mp4)$">
Header set Cache-Control "public"
Header set Expires "Thu, 15 Apr 2010 20:00:00 GMT"
Header unset Last-Modified
</FilesMatch>
#2 hours
<FilesMatch "\.(html|htm|xml|txt|xsl)$">
Header set Cache-Control "max-age=7200, must-revalidate"
</FilesMatch>
<FilesMatch "\.(js|css)$">
SetOutputFilter DEFLATE
Header set Expires "Thu, 15 Apr 2010 20:00:00 GMT"
</FilesMatch>
<FilesMatch ".(eot|ttf|otf|woff)">
<IfModule mod_headers.c>
Header set Access-Control-Allow-Origin "*.domain.com"
</IfModule>
</FilesMatch>
<IfModule mod_deflate.c>
# Force deflate for mangled headers developer.yahoo.com/blogs/ydn/posts/2010/12/pushing-beyond-gzipping/
<IfModule mod_setenvif.c>
<IfModule mod_headers.c>
SetEnvIfNoCase ^(Accept-EncodXng|X-cept-Encoding|X{15}|~{15}|-{15})$ ^((gzip|deflate)\s*,?\s*)+|[X~-]{4,13}$ HAVE_Accept-Encoding
RequestHeader append Accept-Encoding "gzip,deflate" env=HAVE_Accept-Encoding
</IfModule>
</IfModule>
# Compress all output labeled with one of the following MIME-types
# (for Apache versions below 2.3.7, you don't need to enable `mod_filter`
# and can remove the `<IfModule mod_filter.c>` and `</IfModule>` lines as
# `AddOutputFilterByType` is still in the core directives)
<IfModule mod_filter.c>
AddOutputFilterByType DEFLATE application/atom+xml \
application/javascript \
application/json \
application/rss+xml \
application/vnd.ms-fontobject \
application/x-font-ttf \
application/xhtml+xml \
application/xml \
font/opentype \
image/svg+xml \
image/x-icon \
text/css \
text/html \
text/plain \
text/x-component \
text/xml
</IfModule>
</IfModule>
Options +FollowSymlinks
RewriteEngine On
<ifModule mod_headers.c>
Header unset ETag
</ifModule>
FileETag None
<IfModule mod_expires.c>
ExpiresActive on
# Perhaps better to whitelist expires rules? Perhaps.
ExpiresDefault "access plus 1 month"
# cache.appcache needs re-requests in FF 3.6 (thx Remy ~Introducing HTML5)
ExpiresByType text/cache-manifest "access plus 0 seconds"
# Your document html
ExpiresByType text/html "access plus 0 seconds"
# Data
ExpiresByType text/xml "access plus 0 seconds"
ExpiresByType application/xml "access plus 0 seconds"
ExpiresByType application/json "access plus 0 seconds"
# Favicon (cannot be renamed)
ExpiresByType image/x-icon "access plus 1 month"
# Media: images
ExpiresByType image/gif "access plus 1 month"
ExpiresByType image/png "access plus 1 month"
ExpiresByType image/jpg "access plus 1 month"
ExpiresByType image/jpeg "access plus 1 month"
# HTC files (css3pie)
ExpiresByType text/x-component "access plus 1 month"
# Webfonts
ExpiresByType font/truetype "access plus 1 month"
ExpiresByType font/opentype "access plus 1 month"
ExpiresByType application/x-font-woff "access plus 1 month"
ExpiresByType image/svg+xml "access plus 1 month"
ExpiresByType application/vnd.ms-fontobject "access plus 1 month"
# CSS and JavaScript
ExpiresByType text/css "access plus 1 month"
ExpiresByType application/javascript "access plus 1 month"
ExpiresByType text/javascript "access plus 1 month"
<IfModule mod_headers.c>
Header append Cache-Control "public"
</IfModule>
</IfModule>
In GTmatrix in Google pagespeed I have 100% but on Yslow the "Add Expires headers" is 0. I've tried everything but I can't seem to make Yslow work.
Can someone help?
Thanks.

Answer 1

You're setting the expiration to be in the past, which means they expire straight away. The idea behind adding expires headers is that you tell the browser that it doesn't even need to make an http request at all for this resource until some date in the future, instead it should just use the cached copy.
Probably only a good idea to use it on assets you know are not going to change. If you do end up changing an asset with a future expires date you'll need to change the url to it (which you can do by adding a query string on the end like blah.css?1234.
Also check that the expires headers are definitely coming through in the response headers of the assets by inspecting them with your web inspector.