It could work for a RAM upgrade. It worked for the Amiga 500 where it started off with 512mb but then later became the norm to upgrade to 1mb for about £30 at the time. Commodore's mistakes happened after this. The only issue with that is, say the released the xbox with 2gb RAM with a view to upgrade it to 8gb later on, given the low cost of RAM and the money that would be spent to ensuring compatibility issues were ironed out, Would it be that much cheaper than to just have 8gb from day one? I'm sure MS would get the RAM cheaper than we do when they order a few million sets.
Even though it was rare to find someone using an Amiga without a RAM upgrade, it was very rare to find someone who had an FPU (co-processor) installed. This in turn meant few games would make use of one and it kept the prices high.
I know the Amiga was a computer and not a console but most people I knew, used them 95%+ for games.