Why are rich snippets not appearing?

[DanDeceuster]

I'm helping out on a site (www.treadmillreviewguru.com) which formerly had rich snippets appearing in Google. They use hCard markup. All of the markup is visible on the page. The search preview in Google's rich snippets testing tool show a picture, a rating and all that.

However, nothing is appearing in search results. Here is an example page: http://www.treadmillreviewguru.com/nordictrack-treadmill-reviews/nordictrack-commercial-1750-treadmill-reviews-ratings/

This page ranks in the top ten (for me, global results) when I search [nordictrack commercial 1750 treadmill review].

Does anyone know why Google would display the rich snippets a few weeks ago and then not display any at all?

[David_ODonnell]

Google seems to be selective in displaying the rich snippets in results. I have a site that uses ratings snippets and only a tiny percent of the SERPs display with the rating stars. I can't figure out why some display with snippets and some without (# of ratings, rating score to not appear to factor), there must be something in the algorithm that decides this but it is not clear to me.