One problem with setting stories on modern day Earth is that, over time, "modern day Earth" diverges from the real Earth.
So you,me, Clara, Amy and Rory should have;
1. Been enslaved by a Prime Minister called Harold Saxon and future-humans in flying spheres for a year and then had our memories wiped.
2. Had our planet moved, been invaded by Daleks and then had it towed back to the solar system by the Tardis. (Whilst various very un-scientific things also happened) - we should remember that one
3. We were momentarily changed into looking like John Simm.
4. We witnessed David Tennant lighting the 2012 Olympic flame.
5. We should have seen all our clocks turn to zero for a little while.
6. We should have had some pet black cubes for a year and some of us got heart attacks off them and recovered from them.
7. Some of us could have seen various aliens: Autons, Cybermen, Daleks, Slitereen etc. and various spaceships; Attraxi, Titanic, The Valiant etc.
(I'm sure there are others that I've forgotten, and I haven't dared tried to work out what happened "recently" according to Classical Who - didn't the cybermen invade in 1980 - in a Pat Troughton story ? and if so why didn't Jackie Tyler remember them ?

)
The problem with this is that, to relate to the programme, we need modern day Earth to be
our Earth (not a slightly different, increasingly divergent one), and for companions to be at least similar to us when they first meet the Doctor. Hence the tendency for reboot devices such at that at the end of series 3 and crack in series 5 (which at least re-booted Amy to be more like us). Of course enough time has elapsed for us not to bother with questions like "Did Clara get to see Cybermen Ghosts during "Ghost hour" (end of series 2) ?" But you can see why setting stories
away from modern day earth makes the writers job a whole lot easier - there really are only so many different reboot buttons !