I can't speak for ahostmadsen, I can give my input based on the limited experience I had owning the SP4. For me it's SP4 to iPhone that is the issue. Now I know that you can get push email on the SP4 w/ the Mail App, I know you can use Google Calendar so that your iPhone and SP4 stay in sync, I know putting iTunes on the SP4 will take care of syncing music, etc. You even explained that you can download iCloud for Windows to take care of Photos, Contacts, etc. I'm sure you probably can take care of most "Apple Eco" issues on the SP4 through the use of Apps, Programs, etc. That's not the point.
Most of us who aren't using our rMB/SP4 as a work device are limited on the
amount of time we spend on it. We, well I know I, spend 8+ hours a day on a different device for our work duties. When I get off I have limited time on my rMB if any, so convenience is big for me. When you turn on a rMB and sign into iCloud, everything is instantaneous. My contacts, calendar, notes, iMessages, reminders, etc are all right there ready to use as well as mimics what's on my iPhone. I can create a new reminder from my Mac and its automatically on my phone. I can get a text message from a friend, my iPhone can be in another part of the house, yet I will still get the alert on my rMB and can respond right from it. My kids have iPads and use FaceTime, I can answer them from any of my Apple devices. I don't have to put my rMB down and go and locate my phone. This includes phone calls which I can answer right from my rMB. Yeah, Yeah I know, I can get Skype on The SP4 and install Skype on my kids' iPads. That's not the point, the point is convenience.
For some the convenience of everything just working is advantageous. Spending time researching and installing programs to create the best sync environment possible between an iPhone and SP4 may not be desirable for some people. And when they have to make changes for everyone in the house, it's even more of an inconvenience. Now I don't claim to have done much research on synchronization between iPhone and SP4, but from many reviews/impressions I've read, many consider it a disadvantage owning a SP4 over a rMB if you have other Apple products. Doesn't mean it's not possible, just not as seamless. For some people, "Apple Eco" convenience is a big deal. Even more so in a house full of Apple devices