A lot can change in 5 years. Between the elctions of 2001 and 2005, there was 9/11 which took us into a new geopolitical age. There was the War in Afghanistan and then the War in Iraq. There was a whole raft of anti-terrorism legislation. Four years, let alone five, is a long time.
Five years ago, few even knew what subprime mortgage was, the eurozone was confident, and "Boom and Bust" had supposedly been abolished (okay, so I never really believed that one!). Now, after the biggest economic crisis in at least 70 years, we've had free-falling housing prices around the world, giant financial bailouts, and heaving dole queues. A lot can change in 5 years.
We live in a world of 24/7 news bulletins, with an massively expanding internet culture. Life changes pretty rapidly, and governments wield a lot of power (and ours doesn't even have a constitution to control it) over the ordinary citizen. Because the facts keep changing, and because people have a wealth of information at their finger tips, and because we can converse with people on the otherside of the planet with vastly different experiences to us, we need more opportunities to express our political views at the ballot box.
I say reduce the maximum length of Parliament to 3 years. Very few countries have theirs as high as 5, a length of time that is dangerously anti-democratic.