Why do orthoesters react with Grignard reagents, but acetals and ketals don't? My book mentions the synthesis of aldehydes and ketones using alkyl ortho esters. It's called Bodroux-Chichibabin aldehyde synthesis. 

Now, later, the book mentions this: 

R- displaces EtO-, giving an acetal or ketal, which are unreactive with Grignard reagents, so a secondary alcohol is not formed. 

Why do orthoesters react with grignard reagents, but acetals and ketals don't? They have essentially the same functional groups, just two instead of three.
Grignard reactions are performed in ether or THF.
There you have only one -OR group on a carbon and, since it is the solvent, it is not reacting with it.
This shows that not always a -OR group is substituted in a Grignard reaction.

When you have three -OR's on one carbon, the formal positive charge ($\delta+$) on it is higher than when there are only two -OR's. 
Therefore, the reaction proceeds on orthoesters and not on acetals or ketals.