Google only updates their website every month or two, so they may have not spidered your website in time for the latest update. Further, Google has been way off schedule with their updates lately as well.
Also, theres no guarentee that your site will rank well enough to appear on the first page, second page, or even at all.
Session IDs CAN cause problems with spidering, as spiders tend to avoid sites with query strings.
PHP code itself has NOTHING to do with it, as the Googlebot will only get client-side stuff, ie HTML and JavaScript. It can't distinguish between a PHP powered site and say, an ASP site, or even a static HTML one.