Old Apple customers aren't a drain on Apple's financials, even in between the times they're buying new shiny Apple products, but that's Apple.
If you're selling competitive-market hardware like Android phones, you not only need to sell your new phones to new customers, you have to keep the old customers happy enough that 2-3 years from now they'll consider buying a new phone from you, or at very minimum, you're going to have to keep them happy enough they're not saying Really Terrible Things about your support of the old products that trash the willingness of new suckers to buy your products.
For instance, I'm currently a semi-happy Samsung customer, though I've heard rumors they've abandoned my G4 mini. It took me about 8-10 months to go from being a happy owner of a shiny HTC phone to being a disgruntled one (the Aria had a highly customized Android 2.1, locked to the Android Market, and by the time their highly customized 2.2 came out, my phone would no longer accept any software updates, because Google Play was not the same as Android Market.) And Coby? Sure, I knew it was a low-end no-name tablet, but even the manufacturer's web site appeared to have forgotten the product's name by the time I'd opened the box, though on the other hand, Google Play keeps working just fine on it, so until 4.0.4 becomes totally unsupportable, it's doing pretty well.