There is an checking function for fsockopen In Akismet 2.5.3 admin , although there is WordPress HTTP API to connect to Akismet server.
I think it's time to upgrade the check function in admin.php
Here is diff
diff admin.php ~/www/blog/wp-content/plugins/akismet/admin.php
166c166
< if ( !function_exists('fsockopen') || !function_exists('gethostbynamel') ) {
---
> if ( (!function_exists('fsockopen') || !function_exists('gethostbynamel')) && !function_exists('wp_remote_post') ) {
706c706
< if ( !function_exists('fsockopen') || !function_exists('gethostbynamel') )
---
> if ( (!function_exists('fsockopen') || !function_exists('gethostbynamel')) && !function_exists('wp_remote_post') )