Tweetbot’s developers post a link about push notifications:
If you are on the fence about purchasing Tweetbot, don’t buy it just because of push notifications. We aren’t advertising this as a feature until it’s fully working and accessible to everyone. We would like to continue to offer this service for free, however we can’t promise this until we know more about the long term costs. So for now, please remember this is a new feature, it may not fully work and you may not have access to it right away.
This is the kind of approach you want to see developers take. Blatant honesty, full transparency. The guys at Tapbots know what they are doing.