To be ILS or LOC it has to have different minimums for a "localizer only" approach, it is not all that common to have an ILS without other minimums but we have one here at MSO. If you lose any part of the ILS 11 approach you can't do it. You are correct in that the localizer signal will be there and you could navigate with it, but, how low could you go? where is the MAP. The key is how many different minumums does the approach have for different equipment having failed. The LOC mins will be higher than the full ILS mins.
Does anyone have one of these to look at? My guess (that's all it is) is that where an ILS with loc-only minima have identical structures (i.e. the ILS OM and the LOC FAF are the same), in an ILS or LOC chart there may be some differences.
MTPilot, the GS-out (LOC) minimums are always different than the ILS minimums,whether or not the chart is labeled ILS or LOC.
I believe that we are in a transition. However, I also believe a lot of it has to do with how it was checked and certified. I know that really doesn't answer the question "why" but I know sometimes if it listed as a ILS only and the GS is unusable you still get cleared for the "ILS GS unusable to (Insert rwy here)" as opposed to LOC only approach to rwy XX. Does that make any sense at all?