illustrator save as Retina

Hi.

I have an illustrator file, with a vector logo, I can resize it as I want and its looking great.
Now I need to save it for web use, I have saved it as 250px X 250px regular file (100%) in png-24 and 128gif and 256gif its looking fine on a PC/Mac browser.
But when I look at it on a tablet/iPhone/iPad it's get blurred image / logo edge, I have tried to save it for "web use", in png-24 and 128gif and 256gif with a (200%) size, but I still get a bad file to retina, and the illustrator vector file is looking fine, what do I do wrong when saving to/for retina use ?

I got caught out with this as well when I was asked to produce backgrounds for a game app that some of my friends were doing. In my case I had to produce 2 versions of the file and since working in Illustrator it was no problems just to scale down by 50% for the lower res displays. The problem is that IOS just ignores the PPI details inside a file and just goes for the pixel size. I don't know about an html file but that happens when your designing for iPad app. It must be the same but I think it must go with some javascript so that it can tell the browser what type of display is being used. Do a search on the problem but I think I am right.