Thats the point - modern advances has meant we now have more options.
Guitar amp wise, things are pretty much the same as they were back in the 60s. Yes, speaker tech has come on loads... but it seems that guitarists still want something akin to what was available back in the 60s to what the modern speaker can give them. That's cool... that's the tone they are going for. However, the modern modellers can give you that through the modern speakers.
At the end of the day - and I must stress this - there's no wrong or right... backline vs PA power are both valid... and as can be seen from this thread, theres a lot of opinion on both methods. I would argue both are comparably priced - it's just about figuring out what gives the best sound and works best for your own circumstance.