This is not true. Publishing a large block has a cost to the miner due to fact that the larger he makes his block, the greater the chance that his block is orphaned.  This effect is illustrated in Fig. 8 of this paper:



As an example, in the absence of a block size limit, it would cost a miner approximately 100 BTC on average to publish a 128 MB block, assuming a propagation impedance of 7.5 sec / MB.