They've tested all four of those lense at slrgear.com. And it sounds like they liked the Nikon 55-200 just slightly better than the Olympus 40-150. Overall, I think the two kit lens packages are very close, as the 14-45 isn't much different than the 18-55 either:
http://www.slrgear.com/reviews/index.php
It is true that there are still a couple of gaps in the lineup of currently available four thirds lenses on the entry level, but most are being filled. You still aren't going to find the relly low end Vivitar type cheapie lenses. And they could still use a low budget zoom that goes beyond a 300mm equivalent field of view.
Hopefully Sigma will eventually release their 70-300 APO, which for about $200 would end up brigning you to a 600mm equivalent field of view. Right now you can't easily get the 450mm EFOV which that lens and others can give you on the Nikon. The Sigma 135-400, however, is on the way in the next couple of months, delivering a 270-800mm EFOV for around $540.
The other area that has been a bit lacking is low end primes, but Sigma has already adressed much of that, with the 30mm f1.4 and the 105mm f2.8 Macro available now, and the 24mm f1.8 due very soon. The systm does lack the $100 cheapie 50mm available on others, but the 35mm f3.5 Macro for $200 is a nice alternative.
It is true though that there would be more options for older used Nikon lense available for the D50. To use these on the Olympus, you would have to buy an adaptor for around $30 and manually focus:
http://cgi.ebay.com/ws/eBayISAPI.dll...m=280044591095
It will also be easier to rent lense or gear from a camera shop for either Canon or Nikon cameras.
In addition, the Nikon would be better for action or sports shooting. You will tend to have quicker focusing and better focus tracking of moving subjects. The Olympus will focus accurately, but not as quickly. It only has a 3 point auto focus, and it's cameras also do not suppor silent wave motor technology (available in Nikon bodies with some mid range lenses).