This must be a joke? Alonso ended in the gravel trap in Australia.
Not sure what happened to Koba, but probably there was a legit reason he didn't return.
In the case of Hamilton there's no legit reason.
Hamilton failed to meet article 6.6.2 and there was no technical reason that he had to stop. It was just not having enough fuel.
I'm tired of these racism-sayers. Really.. Maybe look at your own or your team's mistakes. That's always lacking with those people saying everything is racism, while they mostly just don't look at their own faults... Btw it's something often happening at McLaren. Remember how many times McLaren failed when Hakkinen and Coulthard drove there? And how many times they failed with Kimi at the wheel?!
Racism is something where you make difference of race.
In this case it's the difference of meeting requirements. If you get into a gravel trap and damage the underside of your car, you don't have to meet 6.6.2. Often you can't even leave the gravel trap! Or if you get an oil leak, or a blown-up engine. Whatever..
If you stop for no other reason than 'not enough fuel' than you have a problem and you're punished to the back of the grid. Simple.
But I'm sure that the FIA also looks if someone drove purposely into a gravel trap, and in the case of Alonso there's no reason a driver would try something dangerous like what happened to him to secure a good position.