You've asked about a specific market though.
What you have to understand, is both brands have required repairs for their workstation products (and will continue to be the case). As for exact statistics in a specific segment/product, you'll have a hard time finding them, if they're available at all, as what I see are aggregate for all the products a vendor sells. For a business, they need a system running, so things like NBD or better support really do matter. Having to carry a MP in, and wait days to get it fixed isn't seen as an attractive solution if there's a problem.
This doesn't surprise me, but they're enterprise grade, which means more than just marketing. They're designed to run in a high availablity environment (24/7/365 operation), so they're equiped with better parts and more extensive validation testing (reliability as well as raw performance).
Exactly. A telephone call works wonders on the selling price with Dell and HP.
As a reminder, to get to 3yrs with the MP, you have to add in the Extended Apple Care, and it's not as good as the warranty offered by Dell (or other vendors such as HP). Some may consider this a moot/unimportant point, but it makes for a more accurate comparision IMO, as exact parity is impossible.
For a business however, this "little" issue is highly important. Not as much to independents though, as they're in a different situation (trade off lower costs for the necessary time input if there is a problem, such as 3rd party upgrades). A business will buy the entire system (includes all desired upgrades) directly from the vendor to have a single point of contact if there's a problem (the entire system is covered under a single warranty).
The statistics are a combination of a vendors entire product lines. So Dell's numbers are noticably affected by the budget systems they sell. Worse yet, the consumer support is an area they cut corners on to save costs (why you get someone from India or Pakistan on the phone after being on hold for a couple of hours during peak call times). It supremely sucks bollocks, but that's part of how they keep the costs down (translates to more $$$ in Dell's coffers, not nearly as much in terms of lower MSRP to the system purchaser).
The Enterprise support side is entirely different however. You won't wait on the phone forever, and the person usually speaks English as their native language. They're also much better trained, as they're expected to deal with unusual situations that're critical to the system owner/user (i.e. know the intimate details of the hardware, and can deal with all of the options, particularly RAID subsystems).
As per Apple, the phone support is quick, but in a specific situation (workstation), there's a chance they won't know what you're talking about (i.e. they don't know much if anything about the RAID Pro card). And the repairs take more time. This may or maynot be of a concern to you, but it is to others (critical actually, especially if that system is earning money). It all comes down to what's important to the user.
Keep in mind vendors like Dell, Apple, HP,... are using ODM suppliers in most, if not all their products (the ODM does the design and manufacturing work), so design and component selection is is left up to the ODM. As a result, product quality has suffered across the board for electronics produced this way (vendor gives up design and production QC for lower costs, as these vendors have a tendency to cut corners anywhere they can). Cheap parts are one of the primary ways that costs are cut to increase the ODM's profit margins, not the vendors. Apple's even suffered from this.
An OEM situation is different, as the vendor supplies the design (PCB artwork and components to be used - BOM = Bill Of Materials). They retain some control (mostly on the design side), but it costs more. There have been cases where component substitutions have occured here as well (parts used that weren't on the BOM or approved by the vendor, such as what's supposed to happen in cases of a supply shortage). But it's hard to sue over it, given the vendor tends to be based in one country, and the OEM in another.
The ideal case, is when a vendor does it all (design and manufacture all their own gear). This allows them to maintain control through every stage that ends in a shipping product. It's also expensive as hell, and only happens in instances where it's a niche product and/or it's performance and reliability are critical. High-end consumer products such as some audio products, medical electronics such as a pace maker, MRI scanner,... , or military equipment are such examples.
And even some of these are going to OEM, though there are some differences here, such as all the suppliers used are in the same country or one that the supplier can be held accountable if there's a problem (multi-country military hardware for example, such as the F-35 - there's parts made all over the place).
preferably with 8x8GB OWC Modules