Hi! I've been communicating with my contact at Arvixe, and here's the situation with the 4.5 upgrade on VPS servers:
1) Because VPS are often customized by their users, a sweeping rollout of 4.5 could create massive havoc for those users who aren't ready for the upgrade, or don't have the manpower available to dedicate to it at this time. (Hi, I'm one of those businesses, and I'm grateful for the option to plan my rollout, instead of having it planned for me.)
2) If you are ready to make the upgrade to your VPS, you can absolutely do so, in one of two ways:
a) DIY - log in through Remote Desktop Connection, and do the installation on your own server
b) Put in a support ticket request to Arvixe at http://support.arvixe.com, or e-mail at support AT arvixe.com, and the support team will install 4.5 for you.
If you have any other questions, please ping me at [email protected], and I'll route your question to the appropriate parties. Thanks!
(For more info on this topic, you can also see this thread on the Arvixe boards: http://forum.arvixe.com/smf/general/net-4-5-framework-on-vpsclass-server/new/#new)