The change in expected utility given constant decisions is the same for any 5% change in probability regardless of where the baseline is for the change. However, that "given constant decisions" criterion may be less likely to hold for a change from 90-95% than it is for a change from 50-55%. If you have to choose whether to risk a negative consequence of not-A in exchange for some benefit, for example, then it matters whether the expected negative utility of not-A just fell by a tenth or by half.