Use head :no_content on the guides as well.

railties/guides/code/getting_started/app/controllers/posts_controller.rb

@@ -62,7 +62,7 @@ def update
     respond_to do |format|
       if @post.update_attributes(params[:post])
         format.html { redirect_to @post, notice: 'Post was successfully updated.' }
-        format.json { head :ok }
+        format.json { head :no_content }
       else
         format.html { render action: "edit" }
         format.json { render json: @post.errors, status: :unprocessable_entity }
@@ -78,7 +78,7 @@ def destroy
 
     respond_to do |format|
       format.html { redirect_to posts_url }
-      format.json { head :ok }
+      format.json { head :no_content }
     end
   end
 end

railties/guides/source/getting_started.textile

@@ -1060,7 +1060,7 @@ def update
     if @post.update_attributes(params[:post])
       format.html  { redirect_to(@post,
                     :notice => 'Post was successfully updated.') }
-      format.json  { render :json => {}, :status => :ok }
+      format.json  { head :no_content }
     else
       format.html  { render :action => "edit" }
       format.json  { render :json => @post.errors,
@@ -1089,7 +1089,7 @@ def destroy
 
   respond_to do |format|
     format.html { redirect_to posts_url }
-    format.json { head :ok }
+    format.json { head :no_content }
   end
 end
 </ruby>