From the very same article:

Unlike Wild 2, Tempel 1 is peppered with impact craters, leading researchers to wonder whether these might be the source of the carbonates and clays.

"We know there's lots of water in the comet," says Lisse. "And Deep Impact did hit between two impact craters. It's possible that those impacts could have created steam, so that the spot where Deep Impact hit was not perfectly pristine. It's not for sure. There's much ambiguity."

Lisse and his colleagues also point out that water is not the only option for producing the minerals. Last year, a team led by Alice Toppani (Lawrence Livermore National Laboratory) showed that carbonates can grow from gases, without liquid water. And other researchers have shown that heating certain minerals in a process called annealing can produce clays — again, no water necessary.

It's also possible that the earlier impact craters were made by carbonaceous bodies encountered somewhere in Tempel's orbit, "contaminating" the eventual Deep Impact site.

It seems, to me at least, far less plausible that radiogenic heating (i.e., deriving from radioactive decay) would be a factor in cometary lifespans, given where they are formed, their size, their density, and their probable homogenous composition. I refer you to the paper (Matson, et. al.) given at this year's Lunar & Planetary Science Conference, news of which probably prompted your remark about radiogenic heating... and point out the huge difference between a planetary satellite with a differentiated interior (i.e., a rocky core) and a "dirty snowball".

One must also take into account the length of time such alleged heating might be available, relative to the life of a comet, as compared to the time life needed to appear on the only place we can -- so far -- prove it did.