Pixel-aligned sharp edges were super important on low-DPI displays, but they are increasingly less important. A one-pixel line on a phone screen is tiny, so most designs will use lines of more than one pixel. A pixel-perfect 3-pixel line doesn't look very different from an anti-aliased 3-pixel line with arbitrary floating-point coordinates on a phone.
Twitter? Because Twitter has been doing that a lot for me recently. It's like all their devs are on mobile or Retina screens and overpowered CPUs and nobody noticed the problem (and resulting processing overhead).
