Check Mags On
The difference is that FR operate very tight schedules and can easily have at least 3, 4 or even 5 return flights per day compared to LS which is usually only 2. Effectively, FR would end up with a huge backlog of indefinite delays if it were not to cancel the disrupted flights.
It is much more manageable for LS however to operate the disrupted flights without causing any severe problems to the rest of its network.
So in my mind it's a no brainer for FR to cancel all the effected flights and promptly inform the relevant passengers whilst keeping everyone else whose flight isn't affected happy. The alternative would be constant delaying and delaying of every single flight across its network and for FR of all airlines would cause absolute havoc for everyone involved.
Neither case is right or wrong as such, it's simply just a difference in the operation between the two airlines.