However for people who's certification is about to expire, perhaps it's not that straight forward.
Thankfully Karl Childs of VMware has produced a couple of Blogs on the VMware Education Blog that are extremely useful.
The first one is New “Bridge” Upgrade Path for Current VCPs, which explains that, any VCP who is two versions behind the most current available version in the same solution track can upgrade to the latest by only taking one exam.
The second one is Certification Insights: Mind the Gap! Your Upgrade Paths Across Tracks, this introduces the new policy:
Crossing certification tracks rule: This policy allows active certification holders to upgrade to a different certification track, as long as the current certification is within two product versions.