Tense for an event that occurs as you read it
Generally speaking, you are right that tenses matter. "Do you know Amy?" or "Do you know where I can get a cheap PC?" are grammatically certainly not the same as "Did you know Amy?" or "Did you know where I can get a cheap PC?"
However, the question at hand, "Did you know that this wait is actually Twitter's fault, not ours?", is different from the aforementioned examples in that the intent of the asker is not to get an answer from you, but rather to provide you with a piece of information. What they are actually saying is:
This wait is Twitter's fault, not ours.
That's all. But note how much harsher it sounds. Rephrasing this as a question is simply a more polite way to convey the same information. In short: the question is rhetorical.
As such, theoretically it could be worded in pretty much any way the asker chooses: "Did you know that...", "Do you know that...", "Would you like to know that...", "May we draw your attention to the fact that...", "Would you mind if we mentioned that...", etc. However, out of the multitude of all possible templates the "Did you know that..." one has emerged to be the most popular one. It is extremely common in spoken conversation, and it is now a well-established template for messages displayed during loading times, from KDE to video games. As nohat succinctly puts it in his answer, it's "a pretty standard formula".
Now, as to why the standard formula has become the one that uses the past and not the present tense, I don't know for certain. However, I will point out that the past tense is often used to make things sound (even) more polite. For example, note the difference between saying "I was wondering if" versus "I am wondering if".
“Did you know…?” is a pretty standard formula for presenting potentially new (usually trivial) information to people. It’s dressing up the presentation of the new information in a question for politeness, which in the context of a real conversation would give the listener an easy opportunity to respond with “No, I didn’t know that—thank you so much for telling me”, or something like that. It’s a polite way to convey information without sounding teacherish, especially if there is a substantial likelihood that the listener already knows that information.
“Do you know…?” would not be a substitution with the same meaning.