And no, the answer is not that they're slippery.
Both brands are owned by the same company, which makes a third, even more iconic product – WD40. It's hard in some ways to believe these brands are related. I always thought of 3-in-One Oil and WD40 as hated rivals and kept them separated on the shelf so they wouldn't get into a fight. But since the same company owns them that makes them kind of like brothers (come to think of it – maybe I should continue to keep them separated).
Among the brands owned by the WD40 Company are:
Blue Works (which makes various lubricants, penetrants, and degreasers)
Hot Shot (carpet stain remover)
X-14 (bathroom cleaner)