Milk = mBTC15
Expensive wine = BTC0.99
Basic Membership = uBTC 999
Silver Membership = mBTC 9.99
Enterprise Membership = BTC 9.99
More likely:
Milk = mBTC15
Expensive wine = BTC0.99
Basic Membership = mBTC 1 (let's be realistic about this one)
Silver Membership = mBTC 10
Enterprise Membership = mBTC 10000 (assuming that a 1000x increase is again reasonable)
In the same way:
Milk = 99c
Expensive wine = $99
Basic membership = $1,000
Silver membership = $10,000
Enterprise membership = $10M
The reality is that people deal with different denominations all the time, just not usually at the same time. If all your groceries are in the mBTC range then they'll all be priced using that range. In the meantime all of the houses for sale will probably be in the kBTC range so will all be priced in that range.
That really is different from what we are talking about here. Your example is more like:
Milk = BTC0.99
Expensive wine = BTC9.99
Basic membership = BTC1,000
Silver membership = BTC10,000
Enterprise membership = BTC10M
As for me having the basic membership priced in uBTC, I'm to make a point, not say that's what it would actually cost. Also keep in mind that in the same way stores use $0.99 instead of $1, Bitcoin stores are likely to use uBTC when it will make their products look cheaper.