There's really not much of a financial incentive for individual miners to include a lot or even any transactions, since at this time the transaction fees are so small. However, a mining pool would have greater incentive. Some of the large pools might be getting 30% of all the blocks found in one day. Current charts show that total transaction fees per day, summed across all blocks for that day, are around 10BTC. So 30% of that is 3BTC or a little over $1800/day at todays exchange, or a nice $675,000 per year at these levels.

Of course if that pool is splitting those fees up amongst a ton of miners who participated in solving those blocks, then it still amounts to very little per miner. But maybe they keep it for themselves??