Go to 12 second mark on this video:
http://www.youtube.com/watch?v=TJOwttgBpzE
see the debris being ejected to the right? chances are one of those, probably the biggest streamer is likely the landing gear.
see how relatively short the distance of the debris field is to the left from the backward explosion?
much of these distance differentials are due to the exponential decrease in distance due to air resistance and gravity. one can easily assume the same was true with the first plane, though the angles for that impact are not available, the results would have been similar, and there is no evidence of streaming debris in the backward flying debris in this video:
http://www.youtube.com/watch?v=r6B7g6mt4Gk
the gear was protected by the fuselage as it was up. if it had been down, there would have been a greater chance of it shearing off. the walls inside the building are thin, but there is obviously the steel framework that it had to avoid, but that is a straight shot through as the framework is not going to prevent the straight through potentiality.
the building is also designed to reduce the sideways forces from the wind. that design will have a dampening effect during the collision and the rebounding potential is reduced accordingly.
the fuselage is designed to provide the potential of a belly landing should the gear not come down. this means it would allow for the plane to absorb the initial impact and the gear would be relatively protected, allowing its inertia to continue forward. it is quite probable the gear was over 25% through the building before the fuselage was stripped away. yes, that is purely a guess, but one can invision the wheels being inside the fuselage traveling into the building a good distance before they themselves touch any part of the building provided they were not in a path that would have them hitting the steel support columns. this opinion is formed from video evidence of plane crashes.