The Community Commons module also provides this functionality, and has this limit set in code.
If you want to change this, my approach would be to create a new Java Action in one of your own modules. Copy the code for the static storeURLtoFileDocument method in Misc.java into the action and tweak the values in there. This means you aren’t changing functionality other parts of your application may be relying on, while allowing you to change values such as increasing the size of the upload where it is a problem.
Hope this helps.