There are two reasons for attaching file in zip folder.
1) I want to save TTI server web space so that saved space can be used by another member for something better
2) TTI dont allow to attach Powerpoint presentation format, so there is no other option but to zip.
Any way these days operating systems do not require the use of Win Zip program to upzip the files. What you need to do it just right click the zip folder you downloaded and click "Extract". The file will be extracted to required location. Or even if you double click zip folder, you will see the file and double click the file again, it will run the file.