Yeah, let's take "Eat a Peach" as an example. Here's the query we run to retrieve the album art for that artist/album pair: http://ws.audioscrobbler.com/1.0/alb...Peach/info.xml

If you look at the result of that query in your web browser, you'll see that this is the <large> image: http://images.amazon.com/images/P/B0...CMZZZZZZZ_.jpg

The image above is 160x159px. Our normal album art (i.e. in the lower right of Kagu) is 125x160px. So there's not much difference there. Last.FM's idea of "large" just isn't very large in that case.

As a similar example, take the artist/album pair (Linkin Park)/"Minutes to Midnight" and the resulting query: http://ws.audioscrobbler.com/1.0/alb...night/info.xml

Here, the large image is this: http://panther1.last.fm/coverart/300x300/3276381.jpg

Which you'll notice is 300x300px, considerably larger than the lower left icon's normal size of 125x160px.

In short, sorry, but I think you just got unlucky. If you can find higher resolution images, you can always dump them in your album dir as a cover.jpg and then you'll have better quality.