Tin hat time but... I'm going to defend him a bit.
Martin has scored lots of goals for Derby as they are a very attacking team and create a lot of chances. He doesn't get that with Scotland as we play a more possession-orientated game so we're maybe not seeing the best of him – far from it in the eyes of probably the majority of fans.
They will argue he offers little movement and struggles on closing opponents down and harrying them etc. Its hard to argue against that. But...
I can see why Strachan picks him. He's a big, strong guy and gives us an alternative – a physical presence. If we want to play it long, he's the target to either hold it up, flick it on or try to get a free-kick. Most importantly of all, he gives us a bit of height and power at set pieces, particularly defensive ones. In some games and also in some phases of games (late on, chasing a goal), we'll need that.
Even with C. Martin there, we are still a couple of taller players, erm, short at set pieces! That showed against Ireland, who carried an aerial threat. We had to defend with the entire team back at free-kicks and corners and rely on the sheer numbers to do the job. The downside of that is no out ball.
In attacking areas, Strachan, McCall and co recognised the height difference between the sides and their instructions against ROI worked as we scored from a short corner.
I reckon Strachan also wants consistency in squad selection – something sadly lacking in the Levein era – and to build a club-like feel to the squad.
Realistically, we don't have too many surefire alternatives - the other contenders all have weaknesses. A few years ago, Goodwillie would have been the one to pick. Not now unfortunately.