And no, the existing lens isn't quite in the same league optically or even close in build to most L lenses, though it is optically among "the best of the rest". However, if the optics truly are improved (which was the point of my original post), it will make it hard for most casual or even fairly serious crop users to justify kicking up to the 70-300 L.
When I first got T2i kit with the 18-55, I also bought the 55-250mm 4-5.6 IS lens. It was my first dSLR. I found both lenses to be horrible. I was surprised that Canon would make such bad lenses. The 55-250 is really bad, even my son who is now using the T2i does not want to use it.
If this is really "the best of the rest", then what lenses are worst then the 55-250?
There must be something wrong with that particular 55-250, as not only I, but almost every other user of that lens gets very good results from it. The attached images are resized, but they were also sharp at full resolution (I don't have access to my main image library right now, otherwise I'd post crops...)
I have one I picked up for my kids to use, and it's great for what it is, and for the cost; but in a direct comparison to any of the L lenses, it doesn't hold up.
I like the images you posted, but with the possible exception of the lizard one, they're not very sharp (that being said, they are small, and it's tough to judge). Which is to be expected of that lens unless stopped down to f8-11 or so. Bokeh is also really nervous, and AF is slow and tends to hunt. None of these things make it a bad lens though. I own one, and it was worth EVERY penny. But to compare it to the 70-300L or any of the 70-200s and try and say it's a better lens, is just not true.