Unfortunately it's not really practical to totally remove that limit. We get an enormous amount of data sent to us and we have to process this data which takes up a lot of computing power (and time). Without going into all the technical details, allowing older scrobbles makes the data crunching a lot slower as we have to go back and update all kinds of old datasets, charts etc. Imagine someone now submitting a track from 2004 and us having to go back and update all the affected weekly, monthly, 3-monthly, 6-monthly and yearly charts. As it stands we now only have to do 2 weeks of backdating which we chose as a compromise between allowing old data and the extra computations required.