Well, perhaps you are right, but correlation does not imply causation so there is quite a bit of room for doubt here. What I would be interested in knowing is:
1) When did large tobacco companies start "improving tobacco" (by the way, I would tend to agree- you start messing with nature, stuff tends to get messed up).
2) Were any studies done prior which compared the incidence of smoking with cancer?
3) How have those statistics changed since?
4) What other major trends were changing at that time? Could anything else plausibly explain the phenomena?