How is semiconductors not a core business for a company that still makes huge profits off mainframes and midranges?? Sure, keep design in house, but you'll lose the flexibility you have. Imagine your research division came up with an amazing new chip design they wanted to work on right away, but were told "Nope, it'll take 6 months to ramp up GlobalFoundries, TSMC, or whatever. Sorry."
Actually, if they can partner with a fabrication company and get the quality they need it will increase their margins. Fabs are expensive and just not worth it until you have massive volumes. Old IBM would buy up a stake (or more likely, keep a stake) their partner and it'll almost certainly be whomever buys their current fabrication ability.
Look at Apple, they don't have a fab... It's odd to me that this issue strikes such a cord, IBM has a checkered history at best in this department. More importantly, the game has shifted from raw cycles and MIPS to performance per watt and while they've done some good stuff in that area a contract fab that can chase the field can probably do better. There was a good block of time, a decade, where IBM owned POWER end to end and it was mediocre compared to the competition. Ideally they can focus more on their designs and make them even better. It's also very clear that they have a new product family they are focusing on, they've made some bold predictions about how big the Watson market will potentially be and if they can really productize that stuff and make it work as good as it worked on Jeopardy without a support staff then I simply don't see why everyone won't have a Watson in 15 years. They are going after that. I'm 14 years removed from IBM but that looks like it's potentially an exciting development.
It's just changing. Answer me this, realistically, what do any PC makes bring to the table any more? Apple brings it all, they are the odd one. HP? Dell? etc..? They take intel parts, they take other 3rdparty parts and integrate them, then they take software from MS and charge a premium on the whole thing. It's a commodity business. It can absolutely be done as well by China and India and other countries. Is there any special skill in assembling those parts? I don't mean this to offend anybody but all of the PC business is going to and should migrate to wherever the labor is the most plentiful and inexpensive. If anything, it seems shocking that all those companies haven't bailed out of that business years ago. Fabing chips in particular seems like a business already designed for that.