@Agra: This happens because liquidity providers also vary. The bid and ask prices displayed by brokers come from liquidity providers.
Examples of liquidity providers include: Deutsche Bank, Citadel, Barclays Bank, UBS, Morgan Stanley, LMAX exchange, Sucden Financial, IG Group, Swissquote, Dukascopy Bank, B2Broker, Boston Prime, Saxobank, Lucid Markets, etc.
Each of the liquidity provider examples above has slightly different bid and ask prices.