Size of imported documents

When clicking to import a document, it appears the information that its size should be 10 MB or less.

So I tried it with a document with a size of about 2,5 MB (word.doc, only plain text, no images at all, no formatting). The system could not manage it: not only uploading was very slow but also it was not able to save the document. Finally I stopped the procedure and deleted the document. :?

So why writing about 10 MB (or less), when the system is not even able to handle a document with 2,5 MB??