Hi Paul
I can appreciate why you'd expect f3.5 to give much more background blur than f22. With a 'standard' or 'telephoto' lens it really does make a big difference. However, with a wide-angle lens it can be very hard to perceive any difference at all.
Let's get one thing straight: regardless of the type of lens, depth of field (DoF) always increases with aperture values. f22 gives more DoF than f3.5: a scientific fact based on the physical properties of all optics.
Look at the flower photos in this link: http://en.wikipedia.org/wiki/Optics#Photography - the f5 photo has way more background blur than the f32 photo, because you get way more DoF at f32. As I say, this happens with all lenses, without exception.
What happens to background blur when you try this experiment at different zoom values is not dependant on optics or science at all. It depends entirely on perception.
Look at the photos halfway-down this page: http://www.luminous-landscape.com/tutorials/dof2.shtml - the smallest zoom value (ie the most wide-angle photo, at 17mm) seems to have huge DoF; it seems as if everything is in focus, and there is little perceptible background blur: in fact the smallest zoom value appears to give no background blur at all. Notice those examples were all shot at the same aperture value (f5.6)
Now have a read of the article. Frankly, I personally think there is a qualitative difference with a very high zoom value lens (like the 400mm in this example) but you see the point: there seems to be no background blur at 17mm, even though there is. This is because there is so much more detail visible in the wide-angle view that the eye accepts the background as 'not blurred', even though it is.
So if you shoot the fountain at 22mm (as you did) it will appear to give you no background blur, whether at f3.5 or f22. This illusion will be even more complete when you're 2m from the fountain than 1m from the fountain. It would, however, have looked very different had you used a higher zoom value (~200mm) and/or got closer to the fountain (~1m): you'd have seen a lot more background blur in your photos.
You will undoubtedly see a more pleasing 'blur' effect with a 200mm prime lens than you will with your 18-200mm zoom, as I've noted in earlier posts, but this is really a matter of taste, not perception. I'd suggest persevering with your current lens until you see the sort of results I've linked to here, before you move on to pastures new.
That's about all I can tell you about it, hope you find it informative!
Cheers
Mick
