I think the traditional concern has been tactical mobility. See battle reports on Grozny, for example. The preconception is that urban terrain forces the tanks to move in predictable paths, while exposing the vulnerable roofs, flanks and rears to enemy anti-tank gunners. In fact, the difficulties suffered by tanks in urban warfare are most often compounded by poor training and employment.

In fact, I believe that armor which is properly supported by infantry and properly employed (i.e. by well trained crews, with adequate maintenance) is extremely effective in a streetfight. The key factor remains training - both by tankers and supporting infantry, however sound employment and numerical superiority can make up for deficits in individual abililty (at the expense of materiel and personnel casualties, increased time and increased collateral damage).