Excursions which, clearly, are conservative probably aren't in question
How do you feel about a "Normal Procedures" takeoff in a 172 with flaps 0 and 70-80 KIAS climb, when the performance charts are based on flaps 10, 56 KIAS climb?
Or a "Normal Procedures" landing at 60-70 KIAS when the performance charts specify 61 KIAS?
Neither are on the conservative side, and there are no performance charts or tables for Normal Procedures, only Short Field. If you're not using the charts anyway, why does it matter if the temperature is outside their range?
(And if you ARE using the charts for Normal Procedures, that's worse, because you can pretty much guarantee that you won't achieve anywhere near the chart figures.)
The big boys don't fly when it's over the limits
I imagine their charts are compiled somewhat differently and they fly the chart speeds every takeoff and landing. Not to mention things like derated takeoffs that require more runway, V1 speeds etc. - they mean that the performance calculations are more critical.
If the runway is short and you find yourself consulting the charts, I would certainly be cautious about exceeding the temperature range. In those circumstances I might be reconsidering even if it is within the range of the charts. But a blanket statement that aircraft must be grounded seems extreme.