f**k off, Fox hardly forced them to use the ADI legs. Fox doesn't give a toss about that kinda stuff.
And the Digitgrade legs on the AI Alien are perfect and extremely Gigeresque, in fact I used to hate them too due to A:R but I like them so much I hope they just Retcon all Aliens with human feet in the first two films (Since we rarely, if ever see their feet.) to have the AI feet.
Fox cares about the Alien's design, haha, next you'll be telling me jet fuel can't melt steel beams.