Would love to know for sure myself!! I assume it is due to some mandate probably issued by Airport Security that all passengers must be in posession of a computer generated boarding pass not those simple but effective plastic cards they use in Luton.
You will also find it impossible to buy DutyFree at GVA without the magnetic strip type boarding pass and we all know how important onsite retail sales are to the profitability of airports nowadays.
Personally speaking, things over here tend to go like clockwork most of the time, and I much prefer GVA-LTN to LTN-GVA where they make you stand in pre-boarding lines relative to your sequence number. That so reminds me of when I was in Primary school (early 70's) and we had to line up in our classes before being allowed back into the building.
Whooaahh!!!