I find that absolutely no different than a pp saying they find it perfectly allowable for their child to read at the table.
We have allowed our children, on occasion to use electronics, to read or to gasp, use the coloring placemats and crayons to keep them entertained during a long wait. All three are no different than the other.
THe "gasp" is pretty dramatic. I never said anything about coloring or drawing or playing tic tac toe (mentioned by another poster) as I find that those activities are generally interactive. I'll ask what the child is drawing, help the child draw, comment on the picture, etc. etc. This can't be done with a child playing on their DS. Usually, the child on the DS is in their own world and will not respond when approached. Therefore, I do think that there is a difference between electronics, reading and coloring.
As in all things, there is moderation. A DS while waiting (with volume muted or earphones) and then put away when food comes is absolutely no different than a child coloring and then putting the crayons away when the food comes or the child that is given a magazine to entertain themselves.
I don't allow my children to read at the table either as it is a singular activity. See above for my comments on coloring.
Moderation. Even the OP, who started this thread, said that occasionally checking texts while at the table has proved to be very beneficial, ie: when their friends texted them they would be late. She turns off her phone, but knows that her calls will be redirected to her husband's phone, whose phone is not turned off.
As for adults, there are numerous different professions where the adults are on call and no, the call cannot wait an hour. For instance, my guess is that if a loved one was having a heart attack, you wouldn't want the cardiologist to have his phone off, saying it can wait an hour. A system failure at VISA would create havoc across the country and people would not be very happy if the techies said "oh, I have to finish my dinner, it can wait an hour." So, yes, there are many, many people out there who need to be attached to their technology and it cannot wait an hour.
My husband checks texts/calls about every 15 minutes, even during dinner. If a call or text comes in, he will check quickly at the table and if something needs more attention, he will excuse himself and go take the call in the lobby or elsewhere.
Actually, the rant was about children who cannot interact not about responsible adults who should use electronics politely (excusing themselves to answer an important call/not talking at the table). My DH has a rather high profile and important job so his phone is on constantly and he does have to take calls often at inopportune times BUT he excuses himself to take the call/text/etc. and extends his apologies to fellow diners when he returns to the table. It is all about how it is done and if the person has manners. He would never take a call at the table and only responds to "important/work related" calls during our family time.