In small startups, one person can do both jobs (maybe not great, but one person can do both).
When you start looking at big companies or well-funded companies, your Vice President of Engineering is usually a glorified project manager who is also a great developer, but in his role as VP of Engineering, his main focus is managing people, keeping projects to their deadlines, building teams, keeping people happy and he barely touches code even though he's a great developer - so in short, very people orientated. In some cases, the VP of Engineering can also be managing multiple teams each with their own dev managers.
The CTO on the other hand has a black belt in Software Architecture, Infrastructure, he understands all the latest technologies, pros and cons of each of them, he has a firm understanding of business, often have some sort of business degree as well, he's a visionary and can often see trends which helps him understand which technologies to use and which to avoid.
In medium sized companies, the CTO is often the architect as well, he lays the foundation, builds the infrastructure and then leave it up to the senior developers to drive the project further. In larger companies, the CTO will work with an Architect and the CTO will drive it from a business point of view, telling the architect in technical terms what he wants, the architect will then take care of the technology constantly running it past the CTO while the CTO's core focus will be working with business to understand their needs, telling them if it can be done, then working with the Dev Manager / VP of Engineering and Architect to explain to them what needs to happen in technical terms - so in short, very business orientated.
Fred Wilson, a Venture Capitalist has this to say about the two roles:
A VP Engineering is ideally a great manager and a great team builder. He or she will be an excellent recruiter, a great communicator, and a great issue resolver. The VP Eng’s job is to make everyone in the engineering organization successful and he or she needs to fix the issues that are getting in the way of success.
A CTO is ideally the strongest technologist in the organization. He or she will be an architect, a thinker, a researcher, a tester and a tinkerer. The CTO is often the technical co-founder if there is one (and you know I think there must be one).
Source: avc.com/2011/10/vp-engineering-vs-cto