Even though the very best receivers today offer performance that's hard to fault, that doesn't mean that receivers are the answer for everyone. High-end audio/video separates can offer performance and features that aren't necessarily available from receivers.
One obvious advantage of separates is that you can precisely match your amplifiers to your loudspeakers. Relatively few A/V receivers can supply 500W per channel, but many monoblock (single channel), 2-channel, and even 3-channel power amplifiers can.
From the standpoint of pure performance, placing power amp(s) in close proximity to the speakers is optimal—and that's impossible with a receiver, although it's easy when you have a separate monoblock amp for each channel.
Of course, the more specialized your requirements, the less likely they'll be accommodated by a receiver, which by its very nature is an attempt to create a one-size-fits-all solution. There is probably no application so specialized that there isn't a specialty separate component manufactured to implement it.
And there's always that indefinable but extremely important element called "pride of ownership." Some people get it from owning only the best, rarest, and/or most expensive components; others get it from combining price and performance without sacrificing satisfaction. Where you fall along that line will probably dictate whether you end up with separates or an AV receiver. The good news is that, whichever option you choose, you can build a very serious high-performance AV system that will repay your investment with years of home theater pleasure.