The two you're referring to were shot at wide open apertures with a $79 lens, that tests horribly compared to most. :-)
They print fine at 8x10 anyway to my eyes (it never ceases to surprise me how much better prints tend to look versus screen images), and I could sharpen them if desired, too. It's all subjective what's acceptable and what's not when you consider things like sharpness.
They were also taken well outside of what you'd want to use for shutter speeds for a hand held photo.
The point is that you can get hand held photos at slower shutter speeds that you could without stabilization. I know I wouldn't have been able to take a sharper photo at 1/20 second at an angle of view equivalent to a 315mm lens on a 35mm camera using a hand held camera without it very often. The rule of thumb would have dicated shutter speeds 10 or 15 times as fast.
Would they have been sharper with a monopod? Maybe. But, depending on where you're shooting, you may not want to use one.
There is no real good standard test to judge the effectiveness of stabilization. But, if you look at some of the tests made by respectable reviewers, most are in agreement that it provides about a 2 stop (or sometimes more) benefit over what they'd get trying to hand hold a camera without it.
Can some people hold a camera steadier than others and get photos that sharp without it? Sure. But, then, they'd be able to go with even slower shutter speeds if desired with it.
I use a flash and tripod, too. But, sometimes, that's just not convenient. IS gives you more flexibilty in what you can get away with if you can't use a flash, or don't want to use a monopod or tripod.
More often than not, I prefer a non-flash photo anyway. Flash can lead to harsher skin tones (too much contrast for my liking) at closer ranges, even when bouncing. For example, this shot was taken with a bounched flash (non-dedicated Sunpak 333 Auto, so the EXIF wont' show a flash was being used).
Or, even when you're in a position where the light is more diffused, you can have problems with things like flash reflections. A lot of that light is going forward, too -- even with the flash head pointed almost straight up.
But, with stabilization, I've got the flexbility of using slower shutter speeds without worrying about lugging a monopod or tripod around, especially while visiting relatives, and I can have the flexibility of a light weight zoom with a good focal range at the same time.
For example, I zoomed in to 85mm for this shot, and took it at 1/15 second without a flash.
Do you sometimes get a touch of blur trying that? Sure. For example, the hand was moving a bit in that image. But, these are perfectly acceptable to my eyes for the print sizes I'd want, and I could sharpen them if desired, too.
The benfits of having it are nice from my perspective, because it gives you more choices. You can still use a brighter lens if desired (and I did take a lot of photos using a brighter 28mm f/2 that same evening, with and without a flash). You can still use a flash if desired (and I took a lot of flash photos that same evening, too).
But, some of my favorites were without a flash, using a lightweight zoom that only has f/4.5 available on it's long end. I've got more choices with Anti-Shake. I don't see a down side to having a camera with it built in.