Yes, every habitable room needs to have an alternative means of escape, generally a window with an opening large enough to climb through. This issue most often comes up with attic conversions where a new room has been created that doesn't meet the Building Regulations, either in terms of the height of the room or the provisions for escape.
If the room does not comply with building regs then it cannot be marketed as a habitable room - if it is described as a habitable room in the sales brochure then that is a misrepresentation and the auctioneer should know better.
It may be possible to replace the rooflight with a dormer window to make the room compliant, depending on location and subject to planning permission.
If you follow this link, you can download a DoE leaflet on attic conversions which gives more informations on escape requirements for rooms with rooflights (Publications & Documents - right hand column):
http://www.environ.ie/en/DevelopmentandHousing/BuildingStandards/