There are a number of very good reasons for going for the 10d as opposed to the 4/3rds system. The choice of already available lenses is one that has already been covered.
I will try to simplify this to make it easy (ish) to understand.
There also the issue of pixel density on image sensors (i.e. how many pixels per square millimetre on either CCD or CMOS chips), with small image sensors as on the 4/3rds system, the amount of pixels required to get an image that will print to a good size and give finer detail can only be increased by using smaller pixels at a greater density, however smaller pixels gather less light therefore need longer exposure, just the same as a smaller aperture needs a longer shutter speed, this would have to be overcome by making them more sensitive and consequently more susceptible to noise, rendering the image less sharp. This means that the chances of the 4/3rds system having a 10 – 12 megapixel sensor in the near future are very slim indeed, so having bought the lenses your choice of cameras when upgrading in the future will be limited.
The issue of sharpness on such high pixel density small sensors is also problematic due to the way in which light entering through a round aperture on the lens is not focussed as a point, but as a small disc (this is known as an Airy disc). This disc gets bigger when stopping down to smaller apertures, so although you increase depth of field, you decrease focus resolution because the Airy disc gets bigger than individual pixels.
Digiscoping with large sensor size DSLR’s suffers a similar problem also, insofar as the sensor in the camera has to be further away from the scope eyepiece so that the light through the scope and camera lens is more spread out in order to fill the size of the sensor, therefore less light is gathered by each pixel and the more projected Airy disc is proportionately bigger.
This problem does exist with film cameras also, but is less visibly apparent because film grain is randomly patterned and not evenly patterned in the way pixels are.
This is an apparent problem on a number of small compact digital cameras with small sensors, as it is not possible to stop down to apertures smaller than f11. The fact that Olympus are designing new lenses across the board for this format does suggest that they have the lens design technology to overcome or alleviate this problem.
At the moment though bigger sensors with lower pixel numbers per square millimetre will give much better quality images.
There are some schools of thought that consider the D60 and 10D sensor pixel density is too high. And tests suggest that the critical sharpness lessens as you stop down beyond f11.
http://www.photography-on-the.net/forum/viewtopic.php?TopicID=2975&page=0
Basically if this is a problem on the 10D it can only be a worse problem on a 4/3rds camera