Clearly Malkin > Staal, but there are scenarios where Staal staying is better than Malkin staying, depending on what offers you get for each and the presumption that Malkin's stock is at his highest now before Crosby plays 60+ games this season and Geno finishes with 80 points as a result.
As for why Malkin does the inconsistent thing, its very simple.
Spoiler: show
The Carolina thing really intrigued me cause when I brought it up, my friend reminded me that Carolina has one of the biggest D prospects in the game (more than Morrow and Despres) in Ryan Murphy.
Eric Staal (C)
Jussi Jokinen (Wing)
Ryan Murphy (D)
1st Round Pick
Eric Staal saves you cap room compared to Geno, Jordan perhaps takes a slight hometown discount as a thank you for getting his brother. You can then roll with
Kunitz/Crosby/Neal
Staal/Staal/Jokinen
or
Kunitz/Crosby/Jokinen
Staal/Staal/Neal
or (if hes cool with it since hes got his brother in the 2C role he wanted)
Kunitz/Crosby/Dupius
Neal/Staal/Jokinen
Cooke/Staal/Kennedy <--- this unit is incredible, the only time Kennedy is remotely tolerable.
With Jokinen and Murphy, combined with Despres and Morrow, Kennedy and Martin both become very expendable and you can shop them for either a new winger to bump Dupius down to 3W in Kennedy's spot (if going with Staals at 2 and 3 C) or a new better-than-most-team's 3C (if going with both Staals in the top 6). As bad as Martin was in the playoffs, he still can get a 2nd line-quality winger or a center somewhere between 2nd and 3rd line level talent, no problemo.
Now, if your top 6 is Staal/Staal/Kunitz/Neal/Crosby/Jokinen, you're starting to look very very large at the forward position. Both top 2 lines are going to have at least 2 wrecking balls in the Staals, Kunitz, and Neal. Crosby won't hit, but hes also incredibly hard to knock off the puck.
As for the D, your D depth could look like:
Orpik/Letang
Michalek/Niskanen
Engelland/Morrow/Despres/Murphy
Goodbye Lovejoy.