Actually the person who wrote this is clearly not a geeky programmer lol. I would say the concept of the ideal world depicted here is closer to reality than you guys think :) I'm moving into a new less known world of programming soon as a career which would be able to prove this. Tasks are becoming much more simplified with advancement of technology today especially, so in terms of the steepness of that slope, it's slowly decreasing it's incline.
If I was to be more geeky, I would say that the logic behind the second diagram is also wrong technically lol, if a bug is found after someone defines it as "all good" I would say it would draw the line to the right, then it's horizontal advancement would stop, it would not go backwards (can't go backwards with a task size, if it's being done wrong, then you just don't advance at all horizontally lol), time spent would make it travel completely perpendicular again to the horizontal plane, and then when it's all fixed, back to a complete horizontal line.