They are the best all in ones available, accross the range (21 & 27) you have the option to get just about any configuaration you could need for all but the most demanding use cases. To be honest with the choice of 8GB to 64GB and up to 3TB fusion drives or 1TB ssd's I can't see why anyone would need to upgrade the internals.
If fiddling around inside a computer is your bag then apple don't make anything for you anymore it's as simple as that, you may not like this direction they have taken but they have taken it and all you can do is put it as an option to discard if buying what you need up front is not what you want to do.