This is true, but given the Arduino does not publish Official gerber and BOM, there's zero chance to recreate the hardware without guessing/reverse engineering. The specs are not version controlled for public consumption.
So the arduino "platform" is not open in that you/I do not have an offical specification to work from.
A simple google search for "arduino bill of materials" found several hits from text, to json, to Excel formats.
If the schematic was only available as pdf, I could understand the complaint that it is not an editable format. There's also Eagle files of schematic and board layout. From that one can make gerbers in a few minutes. Or modify and make something completely different. But in a different comment you said that Eagle files don't count? Why is it that the specific thing you request doesn't count?
The eagle schematic doesn't not have all the mfg part numbers listed. Lots have to be reverse engineered - a good example is the pushbutton switch.
Edit: Also, if you read the first page of their schematic they pretty much say don't use this schematic as a legit source. So if it's open source, my question is where is the "real" source. Answer: they don't publish it. It's locked up internally in the company under a private repo.
On the schematic on the arduino.cc website, the pushbutton switch is labeled "TS42031-160R-TR-7260". A quick google search leads to Omron as the switch manufacturer. Even so, picking a simple button switch from digikey with the right footprint is a trivial task.
The first page of the schematic has a standard disclaimer. It's not different than the standard disclaimer at the top of every open source software source file. (Hardware version: "Reference designs are provided AS IS and WITH ALL FAULTS ....", Software version: "THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND ...")
In the world of electronics, it is normal to label a resistor simply as "10k". Is the resistor from Panasonic? Vishay? Yageo? Is it thin film? carbon? ceramic? It doesn't matter and I don't want to see all that info on a schematic.
The real source is right there on the website. I've personally used their reference designs to make arduino-compatible boards, so I'm positive that all the information is available.
I'm still at a loss as to why you believe that Arduino is not real open source? Is it just because they didn't put a BOM on the website alongside the schematic?
What about the BOM can you not derive from buying an Arduino and looking at it alongside the Atmel datasheets?
Sure, it might be easier and $25 cheaper for you if they published a text file, but it's not like you have to reverse engineer a spaceship to make an Arduino clone or derivative product.
Evidence: there's a wide selection of Arduino compatible boards on the market today.
IMO, publishing the Eagle file is better than publishing the Gerbers. It's roughly the equivalent of publishing source code instead of binaries.
I'm genuinely curious what isn't open-source about Arduino in your opinion?
It's great they provide the eagle files. However when you generate gerber files there are often a lot of settings to configure depending on how you want the files generated. So it's certainly possible for someone (especially a noob) to generate the wrong gerber data set for a given eagle file.
It would be great if they included the eagle file, official bom, and offical gerber data set all in github.
I suspect they do this internally, but they certainly don't give the public access to this information.
So the arduino "platform" is not open in that you/I do not have an offical specification to work from.