In Pro road cycling, a rider, in January, gets three bikes:
one race bike, one spare bike and one TT bike. At CT level, not all riders get three bikes; then, it´s one road race bike and one TT bike, or two road race bikes and no special TT bike. (speaking about non-European CT teams mainly).
Let´s just look at road race bikes for this.
Normally, a rider like Wiggins will have his Number one bike, and rides this bike in training and competition. The reason for this is that after the many hours he spends on this bike, just "gets one" with the bike, and tries to have its setup-up whenever he gets out to ride, no matter if training or competition. He just feels well on this bike, and tries to avoid the spare bike, because even minimal differences of the spare bike compared to the main bike make it difficult for him to feel 100% well on the spare bike.
In a race, he might be forced to switch onto the spare bike, if having a mechanical which can´t be repaired by the mechanic out of the window of the team car. Even then, later in the race, he will want to switch to his Nr 1 bike again, if it has been made working again in the meantime.
So the time you spend on your spare bike are really limited, and it seems not necessary to have SRM on it. It´s for emergency purposes, and even a high budget team like Sky won´t see the need to put SRM on this bike, because at being at about 4000 EUR per SRM, the ratio cost/neccessity is rather bad.