Windows 7 64-bit is currently one of the most secure OSes out there (proven to be more than OS X 10.8, in a recent study)
Don't believe everything you read on the internet.
The MBA, on the other hand, is essentially disposable.
That oft quoted nonsense about Apple making it hard to get inside is a one-sided argument. People fail to quote the many advantages of the more modern Apple designs which include more compact dimensions, increased reliability, increased structural robustness.
Also, quite honestly, although you say the MBA is "disposable", like most Apple hardware products, it will easily last people 5+ years.... by which time it'll be time to move on to the current range of products rather than clinging onto the past.
Carbon-reinforced plastic is way more durable than easily-dented aluminium
An object fell on my Macbook Pro .... little dent at the top of the LCD, but everything still working fine. Its a tool, not a priceless antique. Just get on with using it and forget about minor dings and scratches.