I agree Google shouldn't have omitted the SD card slot from their Nexus series. It's one of many reasons I'll never buy a Nexus device again.
Nobody here is talking about swapping SD cards constantly. What's being talked about is not caring about the capacity of the device you buy. You store apps on the device as there's more than enough space even when they have tiny amounts of memory like 16GB. You store data on one, single, micro SD card. When you run out of space on your micro SD card, you buy a bigger one and copy your data to that.
That way, upgrading your phone is just a matter of swapping the SIM and SD cards. Your data follows you. It "just works". Rather than the inordinately stupid idea, popularized by Apple and slavishly copied by Google, of copying all your data across from one device to the other, either directly, or via the cloud, all umpteen gigabytes of it. That's ridiculous, that's absurd, and manufacturers should recognize that's a massive inconvenience nobody wants.