I will start with the fact that Apple's business model for IOS poses a threat to the integrity and security of Bitcoin. Why because if one gives centralized control over computing devices to a single authority by means of DRM, then one has already set the stage for all sort of attacks against Bitcoin, since the security of Bitcoin depends on individual users having complete control over their computing devices.
Do not get me wrong I do not expect for example a 51% attack against Bitcoin to work at all, in-spite of the efforts of Apple with IOS or Microsoft with Windows 8 RT. Nevertheless it makes very little sense to me why anyone involved with Bitcoin would want to support a business model that poses such a security threat to Bitcoin.
Apart from what Apple has already done namely ban Bitcoin applications which has had minimal impact on Bitcoin only because there are many Bitcoin users that 1) do not use IOS devices for Bitcoin or 2) have jailbroken their devices. Here are some examples from https://en.bitcoin.it/wiki/Weaknesses
1) Cancer Nodes
Turn every iPhone an iPad that has not been jailbroken into a Bitcoin Cancer node.
2) Timejacking http://culubas.blogspot.ca/2011/05/timejacking-bitcoin_802.html
Turn every iPhone an iPad that has not been jailbroken into a Bitcoin timejacking node.
3) Rival/malicious client code
Apple has the market share to pull this off
...
n) any attack where one controls a substantial number of Bitcoin nodes, hash power etc.
These attacks work because Apple and not the end users has control over the software and hardware.
This is not just Apple FUD as Microsoft is moving in he same direction with Windows 8 RT and given Microsoft’s desktop OS market share this can even post a greater threat to Bitcoin. Let us not forget that both these companies are based in the United States and are therefore subject to US law.
Here is an example of a 51% attack by Microsoft: A Windows update that turns every GPU on a Windows machine into a Bitcoin mining node to mine a bad blockchain. To hide itself this could used only say 10% of the GPU power.
These are variations of the Treacherous Computing attack on Bitcoin. http://www.gnu.org/philosophy/can-you-trust.html The warning on Treacherous Computing was first published by Richard Stallman over a decade ago and is extremely relevant to the security of Bitcoin.
If Apple had ban bitcoin there would not be a bitcoin wallet app on their app store, they would get rid of the rest of the bitcoin apps as well. I have heard they don't allow apps which download the blockchain, while I don't support the blocking of any non dangerous apps. Not sure anyone would want a 13 gig wallet app either.
There is no way in hell Microsoft would use windows to attack users and create a botnet. The backlash would pretty much put them out of business or in jail, and would be ineffective in a couple weeks anyway. A GPU botnet would pretty much just burn out gpu's as well. Anyone who has tried to gpu mine without taking the cover off and turning the fan's up could tell you that idea is not gonna fly.