Yeh they are, it is scary just how much force u need to give them some times, if you are really worried about doing in when the mobo is in the case, u can allways take the mobo out, and install the cooler, so that u can have ur hand under the mobo applying opposite force, not the best way to install, as they should install easy without having to do that.
But yeh u need to be firm, go from opposite corner to opposite corner.