I don't know about the technical details of the implementation of those other sites. However, if there are sites that don't use account or cookie prefs to know what you normally search, I would expect nothing less than different results.
Google has been personalizing search results for years to give you information tailored to your needs. Recently, Google search results have been more explicit, displaying search results based on what people in your friend network work have shared. Also, see ratings and reviews on Google Places, for example, where your ratings and those of your friends modify your results giving you better, more personalized information.
Interesting - this appears to be specific to you, as I can't replicate the same query under Chrome non-incognito.
Since it is happening with all extensions disabled, try creating a new user profile for Chrome.
For Linux users:
Exit Google Chrome completely.
Go to Computer or your preferred file manager.
Select Go > Location.
Enter the following directory in the text field:
~/.config/google-chrome/
Locate the folder called "Default" in the directory window that opens and rename it as "Backup default."
Try opening Google Chrome again. A new "Default" folder is automatically created as you start using the browser.
If you wish, you can transfer information from your old user profile to your new one. However, this action is not recommended, since a part of your old profile may be corrupt.
With that in mind, to transfer your old bookmarks, copy the "Bookmarks.bak" file from the "Backup default" folder to your new "Default" folder.
Once moved, rename the file from "Bookmarks.bak" to "Bookmarks" to complete the migration. All other browser data will remain in the "Backup default" folder, but you won't be able to transfer it to your new profile.
For Mac users:
Quit Google Chrome completely. (Command + Q, Force Quit if Chrome is nonresponsive)
Go to the Go menu > Go to Folder.
Enter the following directories in the text field, then press Go.
~/Library/Application Support/Google/Chrome/
Locate the folder called "Default" in the directory window that opens and rename it as "Backup default."
Try opening Google Chrome again. A new "Default" folder is automatically created as you start using the browser.
If you wish, you can transfer information from your old user profile to your new one. However, this action is not recommended, since a part of your old profile may be corrupt.
With that in mind, to transfer your old bookmarks, copy the "Bookmarks.bak" file from the "Backup default" folder to your new "Default" folder.
Once moved, rename the file from "Bookmarks.bak" to "Bookmarks" to complete the migration. All other browser data will remain in the "Backup default" folder, but you won't be able to transfer it to your new profile.
For Windows users:
Exit Google Chrome completely.
Enter the keyboard shortcut Windows key +E to open Windows Explorer or go to Start > Accessories > Windows Explorer.
In the Windows Explorer window that appears enter the following in the address bar.
Windows XP: %USERPROFILE%\Local Settings\Application Data\Google\Chrome\User Data\
Windows Vista/ Windows 7/ Windows 8: %LOCALAPPDATA%\Google\Chrome\User Data\
Locate the folder called "Default" in the directory window that opens and rename it as "Backup default."
Try opening Google Chrome again. A new "Default" folder is automatically created as you start using the browser.
Best Answer
I found an elegant solution to this problem using Google Custom Search.
To see the result in action, go to this custom search engine.
To set up your own version, go to google.com/cse and:
click "create a custom search engine"
put whatever you want on the setup page, but use a nonexistent url for the "sites to search" box
click "next" twice (change the look if you like)
click on the link "change the basics" under "next steps"
at the bottom of the "basics" page, check "search the entire web but emphasize included sites"
uncheck "Show automatic thumbnail"
save changes
click on the name of your search engine at the top of the "basics" page to use it.
To use your search in a URL (to replace your existing search engine):
You'll need to replace the cx variable with the value from your own custom search engine and replace "searchterms" with %s or whatever you usually use in your URL to indicate keyword placement.