NEW YORK (TheStreet) -- I saw Tom Petty and the Heartbreakers play the 1,350-capacity Henry Fonda Theatre last week. Three people deep on the floor, watching Petty lead the band made me feel like I was in the presence of a legend.No doubt I was. The Heartbreakers without Tom Petty cease to exist. On a similar, albeit much lower level, Journey became something other Journey without Steve Perry. Obvious comparison, I know. But Apple ( AAPL) became something other than Apple when Steve Jobs exited Earth and Tim Cook took over as the undisputed leader of the company Jobs built. Obvious, but worth repeating because, no matter how many times we see evidence of Apple's demise under Cook, most people tend to discount the matter's significance. We gave Jobs the credit of a legend when alive, but downplay his impact once he's gone. As if a different Apple can be the same great Apple Jobs ran. It can't be. And, while we probably shouldn't expect Apple to remain exactly the same under Cook and without Jobs, we should do more to guard the latter's legacy and protect the company from spiraling towards run of the mill status.