Inter have so many advantages over Juve when dealing with the mid-table Italian clubs, that it's annoying. In order of importance, these are the reasons why Inter has an advantage over us:
1. They have more money than Juve so they can pay more.
2. They can offer quality players in exchange. None of Genoa, Palermo, Napoli or Sampdoria would like to take our "garbage". None of them would like Salihamidzic, Legrottaglie, Grygera but they'd all want Mancini, Quaresma, Biabiany, Luis Jimenez, Obinna, Suazo and even Burdisso or Rivas.
Players like Poulsen and Amauri are getting lots of playing time and they will never accept to move to Napoli or Sampdoria while guys like Quaresma will do it in order to save their career.
3. These players watch Inter week in week out, they play against them and they all want to be part of a winning machine (at least in domestic level). Also, they know that Inter will pay them bigger wages than Juve.
4. What hurts the most, Napoli, Sampdoria, Genoa etc don't see Inter as their rival so strengthening Inter won't be a problem. But for their ambitions to win the 4th place Juve is a rival and they wouldn't be too happy strengthening a rival

wallbang
Anyway, here is a good example how can Inter strengthen themselves with little money. Take Milito's and Motta's transfer to Inter.
Milito= 25 mln €
Motta = 14 mln €
So Inter have to pay 39m eur for both of them. Instead Inter do this:
- Pay 12 mln €
- Add: Acquafresca 15 mln €, Meggiorini 5 mln €, Bonucci 4 mln €, Bolzoni 3 mln €
In what way can Juve lower a price of 39 mln without losing important players? Look at Felipe Melo's transfer and you'll see how impossible it is for us to do it.