If Intel tells Apple in December-January under NDA that the 3620 and 3640 will ship in July why would Apple buy a contract to buy a years worth of 3530 and 3550 from March '10 to March '11?
They buy parts spaced over time (lots), not all at once, and they pay over time as well.
Now in cases of multiple parts, including those not out, but a date is given to vendors by Intel (NDA or otherwise), they plan accordingly (1. select P/N's desired, 2. quantities purchased). For example, they could buy W3680's now, and go with other hex cores if they chose once they ship (not likely, as it's too many parts, but possible).
As per the newer 35xx parts, they can chose to use those to replace the existing 35xx parts in their respective positions (i.e. base and mid point Quads). So the 2010 base could use the 3530 and mid point Quad with the 3550 giving users a clock increase (and are already available as well).
Even with those contracts none of the large vendors completely dumped their 5500/3500 line ups. Most just increased from 6-10 models to 10-14.
They couldn't, as there's not a full line of hex core SP parts (only the W3680 right now). DP systems they can chose to use either 55xx or 56xx (fits the same boards) to give price points.
For example, Dell offers the L5503 yet, as it still has a place in the market. But they also offer 5680's in the same system (Precision T5500).
Likewise if Intel finds out in November-December can't release all of the 32nm products under contract at the same time .... why wouldn't they hold some of them back until have more fabs running closer to 100% ? For example the core i3-550 didn't ship for 4 months after the others in January.
It wasn't scheduled to release with the others. Intel tends to release a faster part after the initial launch of a line, and this case was no different.
The W3580 is a good example. The time frame was longer than the i3 550, but it still released after the initial launch (fastest at that time was the W3570).
Apple has $40B in the bank. If decide want to wait a bit to get a better contract, they can.
They can, but it's not in their best interest to do so. There's several reasons for this.
- Sales Period (shorter times means less profits, so release delays mean lost $$$)
- Competition (lost sales can occur if the product release is notably later than other vendors)
- Intel deals on quantity, and gives decent pricing to their direct channel partners (it's noticeable, especially when compared to the Distributor channel = volatile; Price stability figures into this)
Even with the fact Macs are meant to run OS X, which is unique to Macs, they're not entirely immune to things like competition, or quarterly sales figures (shareholders can be picky about such things for some strange reason

).