This was actually discussed in the dissenting opinion:
In short, the cell phone acts like a key or portal which can allow the user to access the full treasure trove of records and files that the owner has generated or used on any number of devices. It is not just the device itself and the information it has generated, but the gamut of (often intensely) personal data accessible via the device that gives rise to the significant and unique privacy interests in digital devices. The fact that a suspect may be carrying their house key at the time they are arrested does not justify the police using that key to enter the suspect’s home. In the same way, seizing the key to the user’s digital life should not justify a wholesale intrusion into that realm. Indeed, personal digital devices are becoming as ubiquitous as the house key. Increasingly large numbers of people carry such devices with them everywhere they go (be they cell phones, mobile computers, smart watches, smart glasses, or tablets).
Which then went on to mention that cellphones differ from most forms of evidence in that the may continue to generate evidence after initial siezure, can continue to generate data and/or evidence unknown to the owner, and may impact the privacy of third parties as well, unbeknownst to them.
Also - this is not a blanket inclusion of all cellphone searches incident to arrest. The majority opinion emphatically states that:
The law enforcement objectives served by searches incident to arrest will generally be most compelling in the course of the investigation of crimes that involve, for example, violence or threats of violence, or that in some other way put public safety at risk, such as the robbery in this case, or serious property offences that involve readily disposable property, or drug trafficking. Generally speaking, these types of crimes are most likely to justify some limited search of a cell phone incident to arrest, given the law enforcement objectives. Conversely, a search of a cell phone incident to arrest will generally not be justified in relation to minor offences (emphasis mine).
To summarize, police officers will not be justified in searching a cell phone or similar device incidental to every arrest. Rather, such a search will comply with s. 8 where:
(1) The arrest was lawful;
(2) The search is truly incidental to the arrest in that the police have a reason based on a valid law enforcement purpose to conduct the search, and that reason is objectively reasonable. The valid law enforcement purposes in this context are:
(a) Protecting the police, the accused, or the public;
(b) Preserving evidence; or
(c) Discovering evidence, including locating additional suspects, in situations in which the investigation will be stymied or significantly hampered absent the ability to promptly search the cell phone incident to arrest;
(3) The nature and the extent of the search are tailored to the purpose of the search; and
(4)The police take detailed notes of what they have examined on the device and how it was searched.
And places the onus on the Crown to prove it.
I actually find myself agreeing with this judgement - it seems to me, IMHO, to strike a reasonable balance between the right to privacy and common law principles of warrantless search incidental to arrest. What suspects used to carry on paper is now carried in cellphones, and the law allowing police powers to search papers for a specific purpose should apply also to cellphones, but only for the same purposes. I think this ruling accomplishes that goal.