Steve, thanks for the link. 

I have sought advice.   My machine would be capable of one upgrade (to Snow Leopard), but cannot go to Lion or Mountain Lion for technical reasons.  If I had purchased it 6 mths later, I would have been able to use Lion on it, but, sadly, I cannot.

I was just using my personal experience to back up my point ^^^^ that Apple stuff can date quickly.  For example, they are releasing iPad Air tomorrow and have dropped making iPad 4 (though 2 is still going).  Now, lots of places have iPad 4s in stock still, so you can buy them.  But I'd think getting an iPad Air would be better value, as it is the same price and likely to be supported until at least two newer iPad generations are in circulation, ie 2 yrs on current release rates.

I don't know if phones go out-of-date in this way, as I don't have one.