Well, all the reasons you cited for having the blinking light/timer thing are valid from a storytelling point of view--just as when telling the story of how the hero is battling through the rain and snow to save the lady fair you have to keep reminding the audience that the great big saw is creeping nearer and nearer to Vera. Also, movies and tv shows are made one by one. The writers don't think "oh, such and such had a bomb with a blinking timer, so we'd better just have a plain black box." Plain black box, in any case, doesn't do the job, and the director would tell the writer so if s/he tried it. There has to be something visual to ramp up the tension and make the audience catch their breath. It's not about intelligence or understanding that it's a bomb: this goes deeper than that.
I agree there's scope for more imagination here. I'm sure I saw something a while back (can't remember what it was) where the tension-ramping device took the form of one of those drinking bird thingies. But if it isn't the main point of the plot, if it's just something along the way, then I can see the blinking timer or LED as being a useful and readily understood storytelling device, and useful devices are, well, useful. In other words, from the storyteller's point of view, it ain't broke and therefore doesn't need fixing.
(no subject)
I agree there's scope for more imagination here. I'm sure I saw something a while back (can't remember what it was) where the tension-ramping device took the form of one of those drinking bird thingies. But if it isn't the main point of the plot, if it's just something along the way, then I can see the blinking timer or LED as being a useful and readily understood storytelling device, and useful devices are, well, useful. In other words, from the storyteller's point of view, it ain't broke and therefore doesn't need fixing.