It's mostly because of American airline companies being weird with sports equipment, and if you can fit the bike in a normal sized bag that will go in the hold then it counts as normal luggage.
This is the theory.
Except I have S&S couplers and I can tell you the theory does not work.
The S&S bike cases have no space for shoes, tools, bike clothing, helmet... let alone normal clothing, toiletries, etc.
So you are still going to have to check-in another bag (can't carry tools on, etc) and you're not saving anything in fees.
Also... bikes in boxes with other stuff jammed in tend to weigh quite a bit and still be large, so you're on the cusp of excess baggage anyway, especially for cheaper internal flights.
My solution for my Seven: No S&S, just get a proper sized bike box/bag.
S&S are not really worth it.
That said, at least they have zero impact on frame stiffness, etc. If you've got them your ride isn't affected by them.
I wonder if S&S get around the "no full size bikes on this peak hour train service" type deal?
I remember having to help a US woman in Majorca put her S&S bike together. She could manage the frame but the cable joiners were too hard for her. She needed Di2 brakes :)
A crude packing with rinko type bag (read: fairmean) might work on continental trains i reckon .. just split cables and frame, take wheels apart and tie it to backpack or summat
This is the theory.
Except I have S&S couplers and I can tell you the theory does not work.
The S&S bike cases have no space for shoes, tools, bike clothing, helmet... let alone normal clothing, toiletries, etc.
So you are still going to have to check-in another bag (can't carry tools on, etc) and you're not saving anything in fees.
Also... bikes in boxes with other stuff jammed in tend to weigh quite a bit and still be large, so you're on the cusp of excess baggage anyway, especially for cheaper internal flights.
My solution for my Seven: No S&S, just get a proper sized bike box/bag.
S&S are not really worth it.
That said, at least they have zero impact on frame stiffness, etc. If you've got them your ride isn't affected by them.