Cost is mentioned. An iPad is $500-800. A cloud server is $20/month. A maxxed-out 11" MacBook Air is just under $1800. If you throw it away after 2 years (instead of selling it), that's $75/month. In the same time, you'd spend $40-55/month for the iPad/cloud combo.
Not sure I can follow your calculation. If the iPad is (at most) $800 and the MacBook Air is ~$1800, you'll save roughly $1000 if you go with the iPad. If a cloud server is $20/month than it takes you about 4 years to spend these $1000. Thus if you compare the values within a time span of 2 years, shouldn't the iPad+server combo safe you roughly $500?!
I'm sure I'm missing something.