I believe when it came to decrypting a phone, that is a line they decided they could not cross because of what it would require. I believe, had Artem had an encrypted phone and Apple were asked to decrypt it they would refuse again. It's about what is being asked of them, not about the severity of the crime or situation.
So it is only hypocritical if they help decrypt Artem's phone and not the terrorist's phone and only if Artem's phone requires the same level of work to decrypt. Additionally, the factor of iTunes being affected by the crime having any effect on their willingness to assist law enforcement is pure speculation
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[0] http://arstechnica.com/tech-policy/2016/02/apple-we-tried-to...
"After days of working with the FBI, Apple proposed one final attempt to recover roughly six weeks of data that was locked on the phone." / "With a legal court order, Apple can and does turn over iCloud data."