You are asking two different questions. Vent pipe/flue gas smell and raw gas smell are not the same thing and are not detected the same way.
What is funny is that you have a question about your vent pipes and tricked the gas company to come out and look, and they found a raw gas leak that you would have not know about otherwise!
As far as the vent pipes go, you have a direct vent water heater and a high efficiency gas furnace. They are two completely different items as well. The DV water heater vents straight out to a big cap on the side of your house. All that venting looks fine. The furnace should vent with PVC SCH 40 vent pipe. As far as cracking, look on the pipe for the PVC SCH 40 on it and if so, I would say cracking would be a rare occurance.
There was a vent pipe used on some furnaces in the late early 90's called Plexco that was recalled with a replacement program. Details on that program here: http://www.inspect-ny.com/heat/htpv.htm
Make sure you have a good CO detector, check to make sure you don't have any Plexco (which is unlikely) and rest easy. At least you got rid of that gas leak you did not know you had.
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