I hate to agree here because I love my PC, but I think the assessment is right. PC's are probably on the way out in favor of smaller, more mobile parts. We've already been though the whole "bigger is better" phase in the US. Now, people are moving back towards much more sleek and efficient parts. Unfortunately, PC's aren't exactly known for efficiency. CPU's, by themselves, can use upwards of 130 watts (before overclocking). Now, we've got Graphics cards that use 300-watts or more. To put in perspective, my Acer laptop has a 65-watt power supply. The current technology on desktops is, in my opinion, sort of like a Hummer: Big, brutal, and not very environmentally friendly.
PC's do win on the customization front though. You'll probably never be able to fully customize a tablet down to the last component like you're able to do with a custom desktop PC.
This is going to become more of an enthusiast market than ever in the next several years. Unfortunately, that means that we may not have the options that we once had.