Yes, I guess, but I can't speak for the entire Rails community
But I don't think prepared statements would be used by default on ActiveRecord, but this should be explicited unless setting some option for enabling its use in all cases.
Usually, it is better not to use prepared statements, unless some statement will be batch executed where we can have some performance gains, but that will not be always true. There is also support for the situation that you described regarding binary data.
One of the bad things of using prepared statements if for debugging queries. Under development environment, we can enable config to see the SQL generated queries already with all conversions performed by Rails. When using prepared statements, we would see an output like '["... where a=?", true]' instead of "... where a=1" or "... where a='t'", etc. So it is harder to guess how the driver is converting the objects to SQL values. Specially if you want to run the entire generated SQL in some tool...
In Sequel, it is possible to call a "sql" method to see the generated SQL from a Sequel object. I missed this in ActiveRecord for a long time. I guess this is possible for ActiveRecord in Rails 3 since it is using Arel which takes a similar approach to Sequel, but I'm not sure... Do someone know?