You have some guarantees of access to the present source code (and as jdjb points out, not necessarily), but you're certainly not guaranteed access to changes made in the future by that or other parties like the GPL does. That's the whole point of copyleft and why I prefer it, I don't want to worry if I'll be able to access the features and fixes that will be made by others or if I will be left in the dust. And fair's fair, if you benefited from the work made by others then it's only fair to them to benefit from yours.
Maybe I'm mistaken, but I have the feeling that many -of course, not all and I'm not saying that you do- think that their precious code is so amazing and it will give so much competitive advantage that they need to leave open the option for a closed source version that will make them rich, and that's why they defend "freer" licenses very passionately. Newsflash, it almost surely -like 99,99%- won't happen.
Maybe I'm mistaken, but I have the feeling that many -of course, not all and I'm not saying that you do- think that their precious code is so amazing and it will give so much competitive advantage that they need to leave open the option for a closed source version that will make them rich, and that's why they defend "freer" licenses very passionately. Newsflash, it almost surely -like 99,99%- won't happen.