The net effect? Small developers will target the iPhone first. There will be more new apps on the iPhone then on other platforms and the growth of other platforms will be hampered. Because of this, consumers looking to purchase a phone will see that there are more apps available for the iPhone and based on that make the best choice for them... go with the iPhone.
Why will they do that?
Android is growing and will be out-selling the iPhone and that's not going to reverse. RIM is doing very well for themselves, too.
I totally believe your story, but if there are more Android+BB+Palm phones than iPhones (and more app sales for them then for iPhones) then why wouldn't it be backwards from what you described? Developers will write the cross-platform version first since that will see the most sales there and THEN write the iPhone version.
Right? Why do you think they'll go after the smaller number of sales first? Because that was how it worked in the past? It won't be that way in the future. The iPhone will never be a majority-product. It had a head-start in all this, but it won't last.
So the question becomes, if developers are writing-once-and-running-everywhere BUT the iPhone and then getting to the iPhone second...how is Apple harming anyone with that?