Flat files are databases if you treat them as databases. Advantages of using flat files:
- highly portable
- human readable/directly editable
- zero configuration/administration (sqlite has this advantage too). Security amounts to setting file permissions correctly
Disadvantages:
- time/space efficiency (this doesn't seem matter for your use case though)
- no data integrity checks
- no explicit data types
- tools for working with flat files as databases are (for the most part) much less mature than DBs with a native storage formats
It is wrong to say that you need to write to a DB in order to query your data. There are several tools that let you do that with flat files:
- MySQL CSV Storage Engine
- CSVfix
- MS Log Parser
- TxtSushi (Full disclosure: I wrote this one)
- etc ...
