The loss of the original disc and the loss of the license to use it is in reference to discussions on this forum. When we developed the guidelines for discussion of copyright protected material on these forums, we had to set out what situations we would allow. This is what we came up with to deal with unusual circumstances, such as theft or lost originals. When you purchase software, music, movies, etc., you are buying a license to use that material. For purposes of discussion in these forums, we have tied your license to that original material, whether that original is in the form of a download or a physical disc. Fair use of that material, such as shifting formats or backups, can be discussed as long as you have possession of that original copy.
Copyright law is somewhat fluid when looking at the various laws around the world. A good deal of what we allow in the forums is based on Dutch Home Copy provisions, but we are not quite as lenient as those.
In this situation (a lost original disc), if you have a receipt, or if you have registered your software with the publisher of the software, then you should be speaking with them for a replacement. However, I don't believe a publisher is responsible for your mistake in losing an original, and I can't see that they would be responsible for replacing software for free. They might not even choose to offer you a discount, and still be perfectly within their rights, legally speaking. It wouldn't be very good public relations behavior, but they might not care.
Downloaded material that is purchased, and then lost might be another story...as offering you another download opportunity would cost the company nothing. If you can prove the purchase or registration of the software, a company might be more willing to let you re-download the program.