Just remember one thing. The type of things that happened yesterday happened all the time in the past and will do in the future. The only difference between now and 10 years ago is people watch flightplan, the media report any turn back and blow it out of all proportion into a full scale emergency.
Most are likely to be Pan Pan calls, not emergency calls.
Fire engines and emergency services go out on the runway as a precaution, part of SOP. The media seem to think otherwise.
SOPS's are there for a reason, they work.
The fact is, if Qantas can save a A380 from crashing after a major engine explosion and loss of a lot of the functions, a smell in the cabin is not likely to trouble them that much BUT as a precaution as part of SOP's the checklist says return to nearest airport and land.