FT has an interesting piece out (again) on Apple - Tesla rumor.
http://ftalphaville.ft.com/2015/02/17/2119262/no-one-needs-to-buy-tesla/
Their thought is that Tesla took very little money to build a company where it is today. Which by all accounts, is true. Model S was developed with less than 50% of the money Nissan spent on the Leaf.
Total money spent by Tesla thus far on capX & R&D is somewhere around $2.7 B or so. The original team that introduced Roadster spent $124M and had a headcount of ~500 employees. With Tesla opening the patents already, it is not difficult for a newcomer with LOTS of cash and a huge brand value to develop an EV. There are in fact 10s of local shops that convert your ICE into an EV. Yes, the battery and power train matters. But Apple would not spend $75B to acquire all that. They are much smarter than that.
Also, by 2020, one would expect a few companies to have a successful run at EVs and since outsiders can have a go without learning complex ICEs, Apple does have a chance on its own. If current reports to be believed, Apple already has double the headcount compared to Tesla when Roadster was launched.
I say there is 0% chance Apple will buy Tesla at $75B. Biggest acquisition they have done is Beats I believe. Others, have been in 100s of M to acquire a solution to a problem and they fit it well into their product lineup to make it an excellent feature. I also think Apple is exploring EVs aggressively (just by looking at the hires and size of the team) and may end up doing its own products if its compelling enough.