Red Ring of Death!

[JHeezy]

Try doing this example in Titan HM with the Plumes, this .gif you've provided means NOTHING, you got out of the longer-lasting AoE early which can be dodged with both eyes closed, try it with shorter-lasting AoE's such as Titan HM's Plumes or Allagan Defence System's 'Piercing Laser' for example... totally different story there for people with less-great connections.

People do, on a daily basis.

Probably because both examples you provided are scripted fights and most people will know when said boss will cast said skill and be ready to avoid them. It's simple, get out of the danger zones before the boss stops casting. If you're inside the zones as the boss finishes the cast, you're going to get hit.