The E450 like the E-PL1 mentioned above is an example of something that is common in the photographic market these days. When I first got into photography a camera model would last for years, my first proper camera was Pentax ME Super and they stayed in production for well over five years. These days you're lucky if a new model lasts for more than a year without being superceded. The thing is that the new model often isn't a significant improvement on the old one. Some are nothing more than a firmware upgrade and a new finish.

As a result retailers and manufacturers end up with stocks of the old model that that have to shift. Often the cameras remain current models until stocks are sufficiently depleted. List prices are usually much lower than the new model, but you have to dig around on the manufacturer's website to find them listed as current models.

The E-PL1, for example, is now two generations out of date. And sells for something like half the price of the latest E-PL3.

Just so long as you are not one of those fashion victims who has to have the absolute latest model this is a good thing as you can pick up some great kit at bargain prices, but brand new and with a full warranty. If you are one of those fashion victims of course this is doubly bad news. Not only do you have to buy a new camera at inflated prices every year, but the fact that the old model is still current and discounted means that your outgoing kit is worth a fraction of what you paid for it on the second hand market.

The system is more about the mount than the sensor.

Anyhoo, why would Nikon one of the biggest and most successful camera makers in the world want to get into somebody else's system? Remember other companies have a habit of making Nikon compatible kit, not the other way round.