I certainly touch 50,000 ft more often than once a year but for prayer and services are much more inline with daily and weekly reviews than with specific horizons. Prayer is the time to back off and look to god and let your heart turn to heaven (something that GTD actually helps because of the clear head) I actually have daily checklists to pray at specific times off the day built into my GTD system so I can be sure that my commitment to prayer and God (50,000 ft.) is being taken care of at my next actions (runway).

weekly church services are so similar to my weekly review that I often consider it an extension of them. GTD for me is the major tool I use to push of the "natural man" so I can focus on heaven and purposefully let my mind dwell on those "higher" things, instead of buy bread, fix faucet, and restructure finances. At church, things of a 50,000 ft nature are dealt with and talked about, but what's my purpose fo the planet doesn't change every week, it's just reviewed and reinforced, Just like a weekly review. Where do you think David got the idea?

The yearly suggestion is IMO more about actual reevaluation of your purpose on the planet. Has it changed and you just haven't stopped to really notice? In the religious sense, has a calling from god changed your previously certain future? Did god teach you something that changed where you thought 50,000 ft actually was? Has god shown you 60,000 ft? That's the real purpose fo the yearly 50,000 ft review. Re-center and if it still is the correct center, what needs to happen now? How has your vision changed? How have your goals changed? How should they change? Which projects/goals should you drop because they really have nothing to do with your (hopefully matured) purpose on the planet?
Etc.