Write once, copy many
The problem that Cameron has missed is that software and IT doesn't create many jobs. You have a small (comparatively) team or company that writes an app, or some industrial firmware. That is then published & sold, downloaded millions or billions of times and used everywhere. You still only have quite a small company doing the work - it's just that the company is earning a great deal of money from its success, fame and fortune.
But it's not creating any more jobs.
There is possibly some intangible benefits that accrue to the users: greater efficiency, faster operations, lower costs. But these don't flow back tot he original company that created the software and the benefits confer no competitive advantage on this country as a whole. Even worse, if the company that created this successful app feel they are being too highly taxed, it's very, very easy for it to move to a lower tax (and probably less rainy) country and be just as successful there.
Now consider the manufacturing companies that The Big C is proposing the UK IT "industry" partners. Every widget they make has a human element to it. Sure, the production lines are automated, but they still need people to maintain them, perform some manual operations (even if that number is minimal), pack the physical products, ship and transport them and physically sell them. So each widget produced has some need for workers - the more widgets made, the more workers employed, hence a greater gain for the country where the stuff is made. And if the same country has the skills and industrial base to make the equipment that makes the widgets, you have a double success story.
So while having an IT industry might be trendy, it doesn't do much to directly reduce unemployment and greater success doesn't necessarily lead to more job.. Neither is it particularly permanent in terms of staying and investing in any given country if taxation becomes unfavourably high. So it seems to me, that in this IoT partnership, the Germans have got the tasty end of the candyfloss, and the UK is stuck with the stick.