http://www.xxx.com/abc goes to http://xxx.com/abc ?????

Some internal links in my website, when pointing to www.xxxxxx.com/subcategory1 seem to automatically redirect to xxxxx.com/subcategory1 (note the missing www) .  But links  www.xxxxxx.com/subcategory1/ correctly go to www.xxxxxx.com/subcategory1/ ??

While this doesn;t affect the functionality of the website I've been looking into SEO and am horrified to find that www.domain.com and domain.com are considered separate.  Which I'm probably pretty dim for not realizing earlier but...

My .htaccess looks like this

RewriteEngine on
Options -Indexes +Includes
RewriteRule ^search/page/(.+)/items/(.+)/ /search/index.php?pageNum_Items=$1&totalRows_Items=$2 [L,QSA]
RewriteRule ^(.+)/page/(.+)/items/(.+)/sub/(.+)/$ /$1/index.php?pageNum_Items=$2&totalRows_Items=$3&sub=$4 [L,QSA]
RewriteRule ^([^/]*)/page/([^/]*)/items/([^/]*)/ /$1/index.php?pageNum_Items=$2&totalRows_Items=$3 [L,QSA]
RewriteRule ^(.+)/sub/(.+)/$ /$1/index.php?area=$1&sub=$2 [L,QSA]
RewriteRule ^(.+)/sub/(.+)$ /$1/index.php?area=$1&sub=$2 [L,QSA]
RewriteRule ^(.+)/item/(.+)/$ /$1/index.php?item_id=$2 [L,QSA]
RewriteRule ^(.+)/item/(.+)$ /$1/index.php?item_id=$2 [L,QSA]
RewriteRule ^(.+)/item2/(.+)/$ /$1/index2.php?item_id=$2 [L,QSA]
RewriteRule ^(.+)/item2/(.+)$ /$1/index2.php?item_id=$2 [L,QSA]
RewriteRule ^(.+)/features/(.+)/$ /$1/index.php?feature=$2 [L,QSA]
RewriteRule ^(.+)/features/(.+)$ /$1/index.php?feature=$2 [L,QSA]
RewriteRule ^(.+)/do/(.+)$ /$1/index.php?do=$2 [L,QSA]
RewriteRule ^do/(.+)$ /index.php?do=$1 [L,QSA]
ErrorDocument 403 /v-web/errdocs/403.html
ErrorDocument 401 /v-web/errdocs/401.html
ErrorDocument 500 /v-web/errdocs/500.html
ErrorDocument 400 /v-web/errdocs/400.html
ErrorDocument 404 /v-web/errdocs/404.html
ErrorDocument 404 /v-web/errdocs/404.html

which I'm sure is redundant in some places but can't figure out if this is affecting it.  If this is not the problem can anyone suggest another possibility?