one at a time...lol
control is via infrared...yes the media streamers have pretty systems built into them, but if you have more than two braincells to run together it is pretty easy to integrate a infrared receiver into a htpc. two ways, one cheap, very cheap, and another one slightly more expensive, but easy
1) winlirc software, with a serial infrared receiver which you can make yourself in 5 minutes or buy a premade one for $15
http://lnx.manoweb.com/lirc/?partType=section&partName=buy
fitting it to the case is an exercise for the reader, but most cases have some way of doing this...even if you have to drill a 5mm hole into a drive bay to mount the ir receiver led.
2) use the official microsoft mce remote, which is supported by most frontends. ÂŁ20 overseas, or around R300-400 in s.a. Also easy to integrate the receiver part into a case, dont be so dull
cards with component output...well, if you have a htpc you probably think it is great to play games on your nice big television, so the odds are you already have component output on your graphics card. but I fail to see why you would use component when vga or dvi would do perfectly fine.
If you have a soldering iron, a bit of patience and some spare time, it is relatively easy to hack a quickie cable to work with ati radeon cards to provide proper scart rgb output. maklik. using powerstrip you can program the card for true 720x576 50hz interlaced pal output. Or even widescreen 1024x576. this is all actually not that much of a deal.
compared to the server pc+streamer, well...your server pc would have a big hdd, a tv tuner...so the only diff is the fancy case+remote. I feel that for me, personally, it is easier just to deploy another htpc where it is needed. If I want a streamer I can pick up a secondhand xbox+dvd remote, softmod it and be up and running with xbmc as a streamer+dvd player+ games console for under ÂŁ50. I know the s.a. market is a bit different
have a good day
!