IBM'as systems managers are simply exercising due caution. many large corporate networks run software that's out of the mainstream - possibly developed especially for the company - and there's a perfectly understandable degree of reticewnce to install anything on the operating system which might cause a conflict.
What IBM will almost certainly do is to install SP2 on a batch of machines running the network software. They'll run tests for a while, and when all is well they'll start installing SP2 in batches.
Other big companies will do exactly the same - my larger clients certainly will.
None of this need concern the average home user though, and I hope nobody is deterred by reading the link in spuds post. It doesn't apply to the vast majority of individual users.