It's a completely different format of playing, and some players just aren't suited to it. It would be silly to hold that against them.
A little bit silly I guess, but not completely.
There have been very few batsmen to make the Aussie Test side that haven't played ODIs too. And the ones who have made the Test side without playing a lot of ODIs have been all openers: Langer, Blewett, Katich, Slater and recently Phil Hughes, Phil Jaques too.
Who's the last middle order batsman to play for Australia REGULARLY without playing much for Australia in ODIs? Ummm, well it's Marcus North, and daylight to the next guy. Martin Love probably. Everyone else who's been selected in the Aussie Test middle order has got a decent shot at an ODI spot or leaped some spots in the Test queue based on ODI performance, from Brad Hodge to Michael Bevan to Andrew Symonds, Stuart Law, Tom Moody, Dean Jones, Darren Lehmann, Mike Hussey, Damien Martyn etc etc. all the way up to the Waugh bros, Michael Clarke and Ricky Ponting.
Even if you don't buy the theory, it's silly not to acknowledge that one day performances can help your case for selection. It's one of the 3 ways to get noticed: do well in ODIs/play for NSW/do well vs NSW. Those 3 will let you jump up a few spots in the pecking order