To be fair, White Dwarf is one big steaming pile of advertisement that they charge you, their dear reader, for. It's not surprising that they only show the terrain they're selling. Or the board they're selling. Or pushing the newest armies in their "Battle Reports" section.
Now, as someone who's built the majority of the tables and terrain at the local store, I'll say this for GW's stuff. It's actually quality product. The single Realm of Battle table we have (which was, funnily enough courtesy of Games Workshop when the things were released-- one was sent to every partnership-level independent retailer) has held up better than anything else, and the tables are used at least four times a week. As the person who also maintains the terrain and tables, I appreciate the sturdiness of the Realm Of Battle-- out of the twenty-six tables we have, it's the only one that has never required more than summary touch-ups of paint. Is the Realm of Battle a bit boring? Sure. But it's easy to spice up, it's easy to store, and it's borderline indestructible. The latter really has become a selling point, in my mind-- if you're going to have a single table, then it might actually be worth what they charge you since you'll never have to really maintain the thing the way something you've scratch-built will need to be.
As for GW's terrain-- it's also convenient, and competitively priced. Pegasus Hobby and Woodland Scenics also make quality product, but ultimately, they're not meaningfully cheaper. I've found the Imperial buildings kits to be fairly straightforward to work with provided you've got a file or a rotary tool with a sanding bit handy (GW can't measure 90 degrees for a damn), and hold up quite well. The moonscape set is also a great buy from GW, I think-- it's like $12 and it breaks up the flat surface of a table quite nicely without being terribly obstructive to things like line of sight and maneuvering. Apart from occasionally needing to re-glue random bitz back onto the GW-produced terrain and touch things up from wear and tear, the Citadel terrain requires very little work to keep in good shape.
Now, all that being said, there are a lot of things that GW doesn't make, and other companies do. And there are a lot of things that nobody makes, and you've got to scratch-build. In fact, more items fit the latter description than anything else. If you want any sort of terrain that goes for a table that's not "temperate woodlands" or "urban" in flavor, you're going to have to do it yourself. And that's fine.
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