There is always some truth in some of these commandments but they often get exaggerated and enshrined in law for no good reason. Something that will damage a tyre if carried out at 65mph isn't necessarily going to do any damage at all if carried out at 1mph. Conversely if hitting a fist-sized rock on a back road at 30mph doesn't seem to do any harm to a tyre, why should running up slowly onto a flat block of wood 2" narrower than the tyre do any harm.
Same with lifting front tyres off the ground - no big deal. Nothing will be strained by having to support the weight of the axle while stationary - simply because it is designed to hold it at full downward extension while moving.
Lifting both back wheels off the ground is obviously more problematic because then you are relying on the jacks to be the brakes and some of them won't stand up to a lot of sideways force. However many think that as long as the tyres are on the ground they are OK but once any weight is taken off the wheels, the braking capability is reduced and if the tyres are completely unloaded the braking is zero even though the tyres are still touching.