well,the 5850 overclocks better than the 5870..and when the core is pushed to 1ghz,it well equal and sometimes surpass the 5870 in benchmarks..no wonder ati has increased the price :P
though of course,they could just reduce the 5870's price instead.
They are running out of supplies. They cant sell more 5870s (or 5850s) then they already are.
As long as TSMC doesnt fix things up and Nvidia doenst come up with GT300, AMD / ATI have full control over the market