Sure there are many companies using Lotus Notes, but there is way more enterprise IBM tech & software out there (in use at large companies) than you realize ... WebSphere Portal, IBM Cloud, Rational, Tivoli, DB2, Cognos, Tealeaf, Watson, etc etc
Why do you think for a second that any of that stuff should, would or can go on an iPhone. At least Lotus Notes is a client.
The press release pretty clearly positions Apple devices as front-ends for IBM's big data and cloud offerings.
E.g., compute some "big data analytic" on the IBM server and view it in a dashboard on a mobile Apple device; or interact with client records or job tickets stored in IBM's cloud.
Trust me I've learned all there is to learn about IBM software - while working there.