Walsh has been chosen carefully and correctly by Sky.
At the moment cycling is in the midst of big fallout from the Armstrong case.
Sky themselves have scored a few PR own goals with Rogers and Barry being involved in the Armstrong case, undermining their supposed zero tolerance policy, then some staff having to leave making it look like more than just a couple of bad apples, then the investigation beginning into Leinders which makes them look bad regardless of whether he did anything untoward while at Sky.
David Walsh's reputation on the other hand is riding on a high after being proven right about Armstrong, and being seen as one of the people who stood up to the bully and published some home truths long before they were accepted.
It's a win-win case. Walsh has shown in the recent past that he would like to believe with regards to Sky, and having this journalist who has received credit for his prying into Lance's lies verify that their marginal gains and attention to detail and all the other corporate mantras they spew have led to them becoming the superduper awesome happy friends Clean Team Domination 30, will, they hope, silence a lot of the doubt that surrounds them in the wake of the scandal with Armstrong and while the Leinders case surrounds them, so they'll give him the Tourist Special guide to the team, a bit like going on an official government-sponsored tour of Cuba.
It is true that the doubters as a percentage of audience amongst the casual punters are far fewer, and their doubts less tenaciously held on to, than most hardcore cycling fans, and even more so Clinic regulars. The latter may be more convincingly won over if they did the same piece with Kimmage, as Kimmage has been more cautious in his optimism about Team Sky's über-whiter-than-white image. But most will read a piece about marginal gains from David Walsh as the definitive statement that Sky are authentic, and a piece with Walsh will gain wider circulation faster than a Kimmage piece.