It stands out because it is the least expensive receiver that offers HDMI 1.3 with audio processing. For example, the TX-SR505 and TX-SR575 have HDMI 1.3, but not audio processing. They TX-SR505 and TX-SR575 also do not transcode all inputs (composite, s-video, and component video) to HDMI output for one single connection to your TV. The Onkyo doesn't have a scaler, but it can deinterlace to 480p (same as a standard progressive scan DVD player) but most folks have scaling DVD players now anyway and this feature is not likely to be used.
The TX-SR605 is also the least expensive receiver to offer Dolby Digital Plus, Dolby Digital TrueHD, and DTS-HD decoding from the HD video formats HD DVD and Blu-ray. Only the newest crop of HD DVD and Blu-ray players offer bitstream audio over HDMI of the new audio codecs and in the future it is unlikely that HD DVD and Blu-ray players will have built in decoding for the formats making the receiver handle them.
Lastly, the TX-SR605 has a powered zone 2 feature not found at this price among competitors. Some of the competitors have zone 2 preouts, but no on-board power amplification for the zone 2.
I hope this was helpful and answered your questions.