The Mac Pros are the only Macs in recent memory that I've kept in service for 5+ years, with multiple rounds of disk upgrades (boot SSD + 3TB, then 6TB, currently 12TB), and graphics card and RAM upgrades as well.
If that's important to you, you currently either need a Mac Pro or a hackintosh.
Of course, once the new trash-can Mac Pro ships, there won't be any Macs from Apple like that anymore...