How to interpret the significance of DC specification in SMBus? Why is the VIH value has been fixed to a minimum of 2.1V?
read SMBus 1.1 specifications which has very vague details on the Vih,Vil dependency on Vcc.
It doesn't explain full details but given one para of explanation. I can't put this image into comment, otherwise i could have given comment itself instead of answer. This is not actual answer.