Mark 16::17-18 describes divine abilities believers should possess but not observant to the contrary. You think the same principle of miracles apply today?
Scholars are nearly unanimous that Mark 16:9-20 was not in the original Book of Mark, so I see relatively little need to explain this section in Mark. It is true that these things accompanied the church when it began, so what the Book of Mark has Jesus saying here did happen, but these miraculous gifts were only present in the first generation of the church. If we assume that this passage is inspired, then Jesus is talking about what accompanied the early church, not about what we should be observing in the church today.