For the types of people who build and run skyscrapers, facility operations is a cost center, and regulating authorities don't really care about greenscape. Nobody wants to pay for a staff of gardeners.
That's why when plans get mocked up, the public spaces around commercial buildings are usually lush, but when the building are actually constructed, you see a few shrubs or maybe a few arbor vitae at ground level.
When the local people and regulating bodies care, things are different. The Wal-Mart parking lot in Hilton Head Island, SC is wooded and shaded. The town refuses to issue construction permits that require old growth trees to be cut down -- so there's 60" wide tree in the lot, with a buffer between it and the pavement. Instead of curbs directing water to storm drains, there are mulched beds that absorb alot of storm water. About 15 miles away near I-95, there is another Wal-Mart with the typical construction methods -- bulldoze, flatten and pave everything.