I was refering to the visual styling. HP Slate might not be based on the iPad, but surely it draws on the iPhone/iPod and/or MBP, just as the HP Envy does. Not saying there's anything wrong with that, just that it seems to be a theme in HP's latest products.
Engadget showed images of a HP Slate on 2010-01-06, http://www.engadget.com/2010/01/06/the-hp-slate/
Whilst Engadget were still publishing rumours about an Apple Tablet, http://www.engadget.com/2010/01/20/apple-rumor-roundup-summe..., 2 weeks later. Apple announced their tablet 3 weeks after HP at http://www.engadget.com/2010/01/27/live-from-the-apple-table....
Not conclusive proof but to say that HP were waiting to see Apples spec is wrong; unless you're considering industrial espionage.
Similar info graphically http://www.google.com/trends?q=%22hp+slate%22%2C+%22apple+ip...