There are supporting pegs/feet that come out, you can also see it with the enemy mech's toy detail.
Also, those Linebarrel legs look like they open up to be honest.
The actual concept of mecha (even people) with/using minimal feet support isn't that strange to me, being on the balls of
your feet, extra agility, like a spring in your step. Like a martial artist, for example, me with Muay Tai, they teach you to
stalk with the balls of your feet, and to stay away from falling back on your heels, which can lead to your opponent's
offensive opportunities, and it's just making you slower all round. More balanced, it's easier to check kicks and ride the ring.
Use of the heel should be minimal. (like regaining balance from the turn-around on a kick)
I think this explains it right. http://en.wikipedia.org/wiki/Ball_of_the_foot