element overflowing text but not mackground image

[sergiozambrano]

Time ago I wrote about a technique for creating a transparent css button with only one image, no sprites: http://socialblogsitewebdesign.com/s...t-button-ever/

Basically, in that example a submit input tag "hangs" OUTSIDE the container's width, but using <a> instead of <input type="submit"> won't work:

What is the difference between a label/input combination and a a/span (even a/div) combination that makes the background of the inner element not extending outside the container along with the text?

Thanks