Nessa, it's not a generalization, it's a factual statistic based on actual research. You can probably google it. That stat was from like 2008, from research done by the Barna Group I think. But I'm sure its not much different in 2011.
I understand statistics, but you probably understand how statistics work. I am almost sure that many of the small churches; storefronts; churches that convene in school auditoriums, etc., didn't really figure strongly into statistics. First of all, many of them probably don't even have the numbers to supply to such a study, and second, even more of them probably wouldn't if they did. Legally, churches are required to report certain things, but if you're small, your outreach and evangelism is not going to be easily documented especially if it's not by big-ticket methods.
I mean, evangelism is not an expensive undertaking by any means. Where I come from, if the church can't get a van, the members each volunteer to pick some folks up... it's free to meet together and pray and then go out and invite people, at most you need a tract or flyer... and at the same time, you're also not spending huge amounts on building, instruments or anything else. You're just trying to provide a modest place in the community for saints to gather and worship and receive learn more about Jesus (also evangelism), and keep it warm and lighted (an indirect component of the previous evangelism).
Whether the building or the fancy stuff plays a role in evangelism is also questionable. I mean, no, people don't need to go all out on their church and break the budget. But, if you should do the best you can for God's house. David and Solomon are good examples of this. If we want to live in a nice, clean, permanent place where we can retire to it and relax and be at peace, doesn't God's house deserve to also be a nice, clean, permanent place, where people can count on it to be there and available for them to come and worship, if at all possible? If we're evangelizing and compelling people to come, to where are they going to come? If we're feeding and helping needy people, where should our operations be based? Is there a fixed place where people know that they can come and receive this help? If it's not fixed or stable, does it impact our ability to really be established as a dependable, useful source of aid to those in need? If all of our facilities are rundown and in dire need of renovation, does that also send a message about God's church?
I'm saying that sometimes churches abuse their finances and focus on the wrong things, but all churches do not fit into that category, they are trying to establish their modest, basic, physical facilities, as part of the ministry and mission they are called to carry out.