The laminate can expand due to 2 effects, either heat or moisture.
Heat:
For phenol formaldehyde, coefficient of linear expansivity = 40 x 10e-6 m per m per degree Celsius.
(this is approx, and will be different crosswise to lengthwise, but its a start point)
Assume a temperature range from 0 degree to 40 degree, so max change of temp = 40 degr.
So change of length = 40 x 40 x 10e-6 = 1.6 x 10e-3 m/m
which is 1.6 mm per metre
So in a 5 metre room, expansion would be 5 x 1.6 = 8mm
If the laminate is laid at 20 degr C, then maximum expansion or contraction will be half this value, ie 4mm, or 2mm at each end, so its quite right that there is hardly any expansion under dry conditions.
Damp.
However, the (Hygro) linear expansivity under damp conditions is much greater than under temperature change. Cant find the figures but it easily could be 5 times as much under saturation conditions. So the manufacturers are not lying, they are just being a little over-safe perhaps. Under normal use, the laminate will expand and contract as the humidity of the room changes, and this is invisible. The planks slide along one another.
Thats why you stand the laminate in the room where it is to be laid for a while. You lay it at the average temperature and humidity of the room. This works fine in modern, well insulated houses. Buckling is much more of a problem in older, damp houses, with high temperature and humidity ranges.
The moisture absorption depends on the waterproofness of the laminate, and the more expensive laminates ( with longer guarantees) tend to be more waterproof, and so should need lower gaps at the edges.
Say a radiator leaks. The laminate expands under damp. When they dry out again, they contract. If they are allowed to expand without hitting a wall, then they can re-contract freely, and any damage may be visible as a little delamination, but it may not be too bad. If the gap is not sufficient, the laminate will buckle when it hits the wall. Then the planks could spring apart under the high forces and the click-in edges be damaged. So the gap is necessary.
So, a reasonable compromise in a dry room in a modern house would seem to be say a 5 mm gap at each end. Thats twice as much as actually needed from a heat expansion point of view, and will allow a little bit of moisture expansion too. But in a kitchen say, larger gaps would be advisable, as accidents do happen, and in an old Victorian house, the same applies.