Why are latest versions of v3 unaffected if that line of code isn't present? Is there something else different?
Starting from 3.0.6 aMember uses 'curl' PHP extension to contact PayPal website. If this extension is not enabled, aMember will failback to old method, and then it may be affected by this issue. To check if your webhosting has curl enabled, go to aMember CP -> Version Info, and seek for word "curl" on the page. If you find this word, and you have aMember Pro 3.0.6+ then you do not need to apply any fixes.
According to PayPal, we should also be adding Connection Close code... Should we also modify the code provided in the blog post to have this connection close code mentioned here: https://www.x.com/node/320404 PHP: $header .= "Connection: close\r\n\r\n";