The certificate belongs to EdgeCast, a CDN.
Their job is to serve content on behalf of other companies. The servers that do this typically handle results for hundreds or thousands of different domains, and they have thousands of servers for this purposes scattered all over the world. There are simply too many domains hosted on these servers to give each its own IP, so if they want to serve CDN files over SSL, they have to share a single SSL certificate.
The marginal benefit of serving CDN-hosted files over SSL is minimal, but it's particularly important if you intend to include those files in an SSL-delivered page. Remember that if your page is SSL, then all of the images, scripts, and other resources must also be delivered over SSL, no matter what domain they come from.
Note that none of the SSL domains are the "primary" domain for the site. Instead they're names like
content.truste.com. The companies aren't sharing their own private SSL certificate with all their neighbors; this certificate will not work on
truste.com. Instead they're turning over control of a single-purpose subdomain to edgecast and allowing edgecast to include all these edgecast-specific subdomains into a single certificate specifically for this purpose.
Whom are you trusting with the key to your site? Edgecast, of course. Yes, other companies are also on the same certificate, but the private key is not controlled by you or by any of them; it's controlled by EdgeCast. You're trusting EdgeCast's infrastructure to not allow any other company's content to be visible on your domain. This is the same degree of trust you always are implictly granting to any company you allow to serve content on your behalf. The certificate doesn't really change that relationship.