Why do jets with 3-D thrust vectoring never hover nose up, but instead move slowly forward?
There are limitations in the ability to articulate the thrust vectoring that would limit the ability to hover in space and requires some small amount of forward speed to keep the Sukhoi in a controllable state.  It looks like the RC jet has a vector nozzle that can operate in all directions so that it can be hovered in place like a helicopter, although I imagine the skill level on the part of the operator is pretty high.

My favourite airshow performance of all time was a guy, Wayne Handley, with a monoplane aerobatic machine, the Turbo Raven, with a PT-6 engine, which had a thrust to weight ratio of well over 1:1.  The elevator and rudder surfaces allowed him to control attitude while hanging on the prop, and the ailerons provided anti-torque control.  At Osh in 1998 or 99 I remember him hovering in front of the crowd, moving around in a square box pattern, like outlining a picture frame in the sky, then accelerating straight up until he was a speck.  He stopped doing the act after a crash, from the prop not wanting to come out of ground beta during a descent maneuver, about a year later.  Never seen anything like it since.