Yes, they may be running 10 - 50 kilowatts to no-compromise antennas that amateurs have no hope of duplicating. But consider they're using AM. And they must be heard on pocket radios with tiny ferrite rods. Take away those constraints and use more efficient modes like SSB, CW and narrowband digital techniques, and amateurs can compensate for their lower power and budgets.
As for antennas for 630m, a horizontal dipole, being about 300m long is out of the question. And it wouldn't be any good for groundwave or DX anyway. So you're likely to be using some sort of vertical, even though it may be 1% or less efficient. Hear from amateurs who have had this problem and succeeded on 630m through these links below:
* VK2DX simple 630m antenna
* VK5FQ suburban 630m antenna
* NO3M 630m vertical
* N6LF 630m antenna notes
* 472 kHz.org antenna links
* Kevin Loughlin's 630m magnetic loop (video)
PS: I have written five books on various facets of amateur radio. They are available in electronic or paperback form. Find out more here.